diff --git a/eventbus/acceptance_testing.go b/eventbus/acceptance_testing.go
index ee30d807..9deb0f1e 100644
--- a/eventbus/acceptance_testing.go
+++ b/eventbus/acceptance_testing.go
@@ -72,7 +72,7 @@ func AcceptanceTest(t *testing.T, bus1, bus2 eh.EventBus, timeout time.Duration)
 	ctx := mocks.WithContextOne(context.Background(), "testval")
 
 	// Without handler.
-	id, _ := uuid.Parse("c1138e5f-f6fb-4dd0-8e79-255c6c8d3756")
+	id := uuid.New()
 	timestamp := time.Date(2009, time.November, 10, 23, 0, 0, 0, time.UTC)
 	event1 := eh.NewEventForAggregate(mocks.EventType, &mocks.EventData{Content: "event1"}, timestamp,
 		mocks.AggregateType, id, 1)
diff --git a/eventbus/gcp/eventbus.go b/eventbus/gcp/eventbus.go
index 0dbdc561..7bd1f046 100644
--- a/eventbus/gcp/eventbus.go
+++ b/eventbus/gcp/eventbus.go
@@ -22,10 +22,13 @@ import (
 	"time"
 
 	"cloud.google.com/go/pubsub"
-	"github.com/globalsign/mgo/bson"
 	"github.com/google/uuid"
+	"go.mongodb.org/mongo-driver/bson"
 	"google.golang.org/api/option"
 
+	// Register uuid.UUID as BSON type.
+	_ "github.com/looplab/eventhorizon/types/mongodb"
+
 	eh "github.com/looplab/eventhorizon"
 )
 
@@ -84,11 +87,10 @@ func (b *EventBus) PublishEvent(ctx context.Context, event eh.Event) error {
 
 	// Marshal event data if there is any.
 	if event.Data() != nil {
-		rawData, err := bson.Marshal(event.Data())
-		if err != nil {
+		var err error
+		if e.RawData, err = bson.Marshal(event.Data()); err != nil {
 			return errors.New("could not marshal event data: " + err.Error())
 		}
-		e.RawData = bson.Raw{Kind: 3, Data: rawData}
 	}
 
 	// Marshal the event (using BSON for now).
@@ -97,13 +99,10 @@ func (b *EventBus) PublishEvent(ctx context.Context, event eh.Event) error {
 		return errors.New("could not marshal event: " + err.Error())
 	}
 
-	// NOTE: Using a new context here.
-	// TODO: Why?
-	publishCtx := context.Background()
-	res := b.topic.Publish(publishCtx, &pubsub.Message{
+	res := b.topic.Publish(ctx, &pubsub.Message{
 		Data: data,
 	})
-	if _, err := res.Get(publishCtx); err != nil {
+	if _, err := res.Get(ctx); err != nil {
 		return errors.New("could not publish event: " + err.Error())
 	}
 
@@ -185,13 +184,9 @@ func (b *EventBus) handle(m eh.EventMatcher, h eh.EventHandler, sub *pubsub.Subs
 
 func (b *EventBus) handler(m eh.EventMatcher, h eh.EventHandler) func(ctx context.Context, msg *pubsub.Message) {
 	return func(ctx context.Context, msg *pubsub.Message) {
-		// Manually decode the raw BSON event.
-		data := bson.Raw{
-			Kind: 3,
-			Data: msg.Data,
-		}
+		// Decode the raw BSON event data.
 		var e evt
-		if err := data.Unmarshal(&e); err != nil {
+		if err := bson.Unmarshal(msg.Data, &e); err != nil {
 			select {
 			case b.errCh <- eh.EventBusError{Err: errors.New("could not unmarshal event: " + err.Error()), Ctx: ctx}:
 			default:
@@ -200,22 +195,25 @@ func (b *EventBus) handler(m eh.EventMatcher, h eh.EventHandler) func(ctx contex
 			return
 		}
 
-		// Create an event of the correct type.
-		if data, err := eh.CreateEventData(e.EventType); err == nil {
-			// Manually decode the raw BSON event.
-			if err := e.RawData.Unmarshal(data); err != nil {
-				select {
-				case b.errCh <- eh.EventBusError{Err: errors.New("could not unmarshal event data: " + err.Error()), Ctx: ctx}:
-				default:
-				}
-				msg.Nack()
-				return
+		// Create an event of the correct type and decode from raw BSON.
+		var err error
+		if e.data, err = eh.CreateEventData(e.EventType); err != nil {
+			select {
+			case b.errCh <- eh.EventBusError{Err: errors.New("could not create event data: " + err.Error()), Ctx: ctx}:
+			default:
 			}
-
-			// Set concrete event and zero out the decoded event.
-			e.data = data
-			e.RawData = bson.Raw{}
+			msg.Nack()
+			return
+		}
+		if err := bson.Unmarshal(e.RawData, e.data); err != nil {
+			select {
+			case b.errCh <- eh.EventBusError{Err: errors.New("could not unmarshal event data: " + err.Error()), Ctx: ctx}:
+			default:
+			}
+			msg.Nack()
+			return
 		}
+		e.RawData = nil
 
 		event := event{evt: e}
 		ctx = eh.UnmarshalContext(e.Context)
diff --git a/eventstore/acceptanece_testing.go b/eventstore/acceptanece_testing.go
index 2377ad9d..9791daea 100644
--- a/eventstore/acceptanece_testing.go
+++ b/eventstore/acceptanece_testing.go
@@ -40,14 +40,14 @@ func AcceptanceTest(t *testing.T, ctx context.Context, store eh.EventStore) []eh
 
 	ctx = context.WithValue(ctx, "testkey", "testval")
 
-	t.Log("save no events")
+	// Save no events.
 	err := store.Save(ctx, []eh.Event{}, 0)
 	if esErr, ok := err.(eh.EventStoreError); !ok || esErr.Err != eh.ErrNoEventsToAppend {
 		t.Error("there shoud be a ErrNoEventsToAppend error:", err)
 	}
 
-	t.Log("save event, version 1")
-	id, _ := uuid.Parse("c1138e5f-f6fb-4dd0-8e79-255c6c8d3756")
+	// Save event, version 1.
+	id := uuid.New()
 	timestamp := time.Date(2009, time.November, 10, 23, 0, 0, 0, time.UTC)
 	event1 := eh.NewEventForAggregate(mocks.EventType, &mocks.EventData{Content: "event1"},
 		timestamp, mocks.AggregateType, id, 1)
@@ -60,13 +60,13 @@ func AcceptanceTest(t *testing.T, ctx context.Context, store eh.EventStore) []eh
 	// 	t.Error("the context should be correct:", agg.Context)
 	// }
 
-	t.Log("try to save same event twice")
+	// Try to save same event twice.
 	err = store.Save(ctx, []eh.Event{event1}, 1)
 	if esErr, ok := err.(eh.EventStoreError); !ok || esErr.Err != eh.ErrIncorrectEventVersion {
 		t.Error("there should be a ErrIncerrectEventVersion error:", err)
 	}
 
-	t.Log("save event, version 2")
+	// Save event, version 2.
 	event2 := eh.NewEventForAggregate(mocks.EventType, &mocks.EventData{Content: "event2"},
 		timestamp, mocks.AggregateType, id, 2)
 	err = store.Save(ctx, []eh.Event{event2}, 1)
@@ -75,7 +75,7 @@ func AcceptanceTest(t *testing.T, ctx context.Context, store eh.EventStore) []eh
 	}
 	savedEvents = append(savedEvents, event2)
 
-	t.Log("save event without data, version 3")
+	// Save event without data, version 3.
 	event3 := eh.NewEventForAggregate(mocks.EventOtherType, nil, timestamp,
 		mocks.AggregateType, id, 3)
 	err = store.Save(ctx, []eh.Event{event3}, 2)
@@ -84,7 +84,7 @@ func AcceptanceTest(t *testing.T, ctx context.Context, store eh.EventStore) []eh
 	}
 	savedEvents = append(savedEvents, event3)
 
-	t.Log("save multiple events, version 4, 5 and 6")
+	// Save multiple events, version 4,5 and 6.
 	event4 := eh.NewEventForAggregate(mocks.EventOtherType, nil, timestamp,
 		mocks.AggregateType, id, 4)
 	event5 := eh.NewEventForAggregate(mocks.EventOtherType, nil, timestamp,
@@ -97,8 +97,8 @@ func AcceptanceTest(t *testing.T, ctx context.Context, store eh.EventStore) []eh
 	}
 	savedEvents = append(savedEvents, event4, event5, event6)
 
-	t.Log("save event for another aggregate")
-	id2, _ := uuid.Parse("c1138e5e-f6fb-4dd0-8e79-255c6c8d3756")
+	// Save event for another aggregate.
+	id2 := uuid.New()
 	event7 := eh.NewEventForAggregate(mocks.EventType, &mocks.EventData{Content: "event7"},
 		timestamp, mocks.AggregateType, id2, 1)
 	err = store.Save(ctx, []eh.Event{event7}, 0)
@@ -107,7 +107,7 @@ func AcceptanceTest(t *testing.T, ctx context.Context, store eh.EventStore) []eh
 	}
 	savedEvents = append(savedEvents, event7)
 
-	t.Log("load events for non-existing aggregate")
+	// Load events for non-existing aggregate.
 	events, err := store.Load(ctx, uuid.New())
 	if err != nil {
 		t.Error("there should be no error:", err)
@@ -116,7 +116,7 @@ func AcceptanceTest(t *testing.T, ctx context.Context, store eh.EventStore) []eh
 		t.Error("there should be no loaded events:", eventsToString(events))
 	}
 
-	t.Log("load events")
+	// Load events.
 	events, err = store.Load(ctx, id)
 	if err != nil {
 		t.Error("there should be no error:", err)
@@ -136,7 +136,7 @@ func AcceptanceTest(t *testing.T, ctx context.Context, store eh.EventStore) []eh
 		}
 	}
 
-	t.Log("load events for another aggregate")
+	// Load events for another aggregate.
 	events, err = store.Load(ctx, id2)
 	if err != nil {
 		t.Error("there should be no error:", err)
@@ -167,8 +167,8 @@ func AcceptanceTest(t *testing.T, ctx context.Context, store eh.EventStore) []eh
 func MaintainerAcceptanceTest(t *testing.T, ctx context.Context, store eh.EventStoreMaintainer) {
 	ctx = context.WithValue(ctx, "testkey", "testval")
 
-	t.Log("save some events")
-	id, _ := uuid.Parse("c1138e5f-f6fb-4dd0-8e79-255c6c8d3757")
+	// Save some events.
+	id := uuid.New()
 	timestamp := time.Date(2009, time.November, 10, 23, 0, 0, 0, time.UTC)
 	event1 := eh.NewEventForAggregate(mocks.EventType, &mocks.EventData{Content: "event1"},
 		timestamp, mocks.AggregateType, id, 1)
@@ -180,21 +180,21 @@ func MaintainerAcceptanceTest(t *testing.T, ctx context.Context, store eh.EventS
 		t.Error("there should be no error:", err)
 	}
 
-	t.Log("replace event, no aggregate")
+	// Replace event, no aggregate.
 	eventWithoutAggregate := eh.NewEventForAggregate(mocks.EventType, &mocks.EventData{Content: "event"},
 		timestamp, mocks.AggregateType, uuid.New(), 1)
 	if err := store.Replace(ctx, eventWithoutAggregate); err != eh.ErrAggregateNotFound {
 		t.Error("there should be an aggregate not found error:", err)
 	}
 
-	t.Log("replace event, no event version")
+	// Replace event, no event version.
 	eventWithoutVersion := eh.NewEventForAggregate(mocks.EventType, &mocks.EventData{Content: "event20"},
 		timestamp, mocks.AggregateType, id, 20)
 	if err := store.Replace(ctx, eventWithoutVersion); err != eh.ErrInvalidEvent {
 		t.Error("there should be an invalid event error:", err)
 	}
 
-	t.Log("replace event")
+	// Replace event.
 	event2Mod := eh.NewEventForAggregate(mocks.EventType, &mocks.EventData{Content: "event2_mod"},
 		timestamp, mocks.AggregateType, id, 2)
 	if err := store.Replace(ctx, event2Mod); err != nil {
@@ -218,7 +218,7 @@ func MaintainerAcceptanceTest(t *testing.T, ctx context.Context, store eh.EventS
 		}
 	}
 
-	t.Log("save events of the old type")
+	// Save events of the old type.
 	oldEventType := eh.EventType("old_event_type")
 	id1 := uuid.New()
 	oldEvent1 := eh.NewEventForAggregate(oldEventType, nil, timestamp,
@@ -233,7 +233,7 @@ func MaintainerAcceptanceTest(t *testing.T, ctx context.Context, store eh.EventS
 		t.Error("there should be no error:", err)
 	}
 
-	t.Log("rename events to the new type")
+	// Rename events to the new type.
 	newEventType := eh.EventType("new_event_type")
 	if err := store.RenameEvent(ctx, oldEventType, newEventType); err != nil {
 		t.Error("there should be no error:", err)
diff --git a/eventstore/memory/eventstore_test.go b/eventstore/memory/eventstore_test.go
index f8bca998..3a0a8074 100644
--- a/eventstore/memory/eventstore_test.go
+++ b/eventstore/memory/eventstore_test.go
@@ -28,15 +28,9 @@ func TestEventStore(t *testing.T) {
 		t.Fatal("there should be a store")
 	}
 
-	// Run the actual test suite.
-
-	t.Log("event store with default namespace")
+	// Run the actual test suite, both for default and custom namespace.
 	eventstore.AcceptanceTest(t, context.Background(), store)
-
-	t.Log("event store with other namespace")
 	ctx := eh.NewContextWithNamespace(context.Background(), "ns")
 	eventstore.AcceptanceTest(t, ctx, store)
-
-	t.Log("event store maintainer")
 	eventstore.MaintainerAcceptanceTest(t, context.Background(), store)
 }
diff --git a/eventstore/mongodb/eventstore.go b/eventstore/mongodb/eventstore.go
index 5d92e87b..48be0e2c 100644
--- a/eventstore/mongodb/eventstore.go
+++ b/eventstore/mongodb/eventstore.go
@@ -20,9 +20,16 @@ import (
 	"fmt"
 	"time"
 
-	"github.com/globalsign/mgo"
-	"github.com/globalsign/mgo/bson"
 	"github.com/google/uuid"
+	"go.mongodb.org/mongo-driver/bson"
+	"go.mongodb.org/mongo-driver/mongo"
+	"go.mongodb.org/mongo-driver/mongo/options"
+	"go.mongodb.org/mongo-driver/mongo/readconcern"
+	"go.mongodb.org/mongo-driver/mongo/readpref"
+	"go.mongodb.org/mongo-driver/mongo/writeconcern"
+
+	// Register uuid.UUID as BSON type.
+	_ "github.com/looplab/eventhorizon/types/mongodb"
 
 	eh "github.com/looplab/eventhorizon"
 )
@@ -30,8 +37,8 @@ import (
 // ErrCouldNotDialDB is when the database could not be dialed.
 var ErrCouldNotDialDB = errors.New("could not dial database")
 
-// ErrNoDBSession is when no database session is set.
-var ErrNoDBSession = errors.New("no database session")
+// ErrNoDBClient is when no database client is set.
+var ErrNoDBClient = errors.New("no database client")
 
 // ErrCouldNotClearDB is when the database could not be cleared.
 var ErrCouldNotClearDB = errors.New("could not clear database")
@@ -50,31 +57,32 @@ var ErrCouldNotSaveAggregate = errors.New("could not save aggregate")
 
 // EventStore implements an EventStore for MongoDB.
 type EventStore struct {
-	session  *mgo.Session
+	client   *mongo.Client
 	dbPrefix string
 }
 
-// NewEventStore creates a new EventStore.
-func NewEventStore(url, dbPrefix string) (*EventStore, error) {
-	session, err := mgo.Dial(url)
+// NewEventStore creates a new EventStore with a MongoDB URI: `mongodb://hostname`.
+func NewEventStore(uri, dbPrefix string) (*EventStore, error) {
+	opts := options.Client().ApplyURI(uri)
+	opts.SetWriteConcern(writeconcern.New(writeconcern.WMajority()))
+	opts.SetReadConcern(readconcern.Majority())
+	opts.SetReadPreference(readpref.Primary())
+	client, err := mongo.Connect(context.TODO(), opts)
 	if err != nil {
 		return nil, ErrCouldNotDialDB
 	}
 
-	session.SetMode(mgo.Strong, true)
-	session.SetSafe(&mgo.Safe{W: 1})
-
-	return NewEventStoreWithSession(session, dbPrefix)
+	return NewEventStoreWithClient(client, dbPrefix)
 }
 
-// NewEventStoreWithSession creates a new EventStore with a session.
-func NewEventStoreWithSession(session *mgo.Session, dbPrefix string) (*EventStore, error) {
-	if session == nil {
-		return nil, ErrNoDBSession
+// NewEventStoreWithClient creates a new EventStore with a client.
+func NewEventStoreWithClient(client *mongo.Client, dbPrefix string) (*EventStore, error) {
+	if client == nil {
+		return nil, ErrNoDBClient
 	}
 
 	s := &EventStore{
-		session:  session,
+		client:   client,
 		dbPrefix: dbPrefix,
 	}
 
@@ -90,9 +98,6 @@ func (s *EventStore) Save(ctx context.Context, events []eh.Event, originalVersio
 		}
 	}
 
-	sess := s.session.Copy()
-	defer sess.Close()
-
 	// Build all event records, with incrementing versions starting from the
 	// original aggregate version.
 	dbEvents := make([]dbEvent, len(events))
@@ -124,18 +129,20 @@ func (s *EventStore) Save(ctx context.Context, events []eh.Event, originalVersio
 		version++
 	}
 
+	c := s.client.Database(s.dbName(ctx)).Collection("events")
+
 	// Either insert a new aggregate or append to an existing.
 	if originalVersion == 0 {
 		aggregate := aggregateRecord{
-			AggregateID: aggregateID.String(),
+			AggregateID: aggregateID,
 			Version:     len(dbEvents),
 			Events:      dbEvents,
 		}
 
-		if err := sess.DB(s.dbName(ctx)).C("events").Insert(aggregate); err != nil {
+		if _, err := c.InsertOne(ctx, aggregate); err != nil {
 			return eh.EventStoreError{
-				BaseErr:   err,
 				Err:       ErrCouldNotSaveAggregate,
+				BaseErr:   err,
 				Namespace: eh.NamespaceFromContext(ctx),
 			}
 		}
@@ -143,9 +150,9 @@ func (s *EventStore) Save(ctx context.Context, events []eh.Event, originalVersio
 		// Increment aggregate version on insert of new event record, and
 		// only insert if version of aggregate is matching (ie not changed
 		// since loading the aggregate).
-		if err := sess.DB(s.dbName(ctx)).C("events").Update(
+		if _, err := c.UpdateOne(ctx,
 			bson.M{
-				"_id":     aggregateID.String(),
+				"_id":     aggregateID,
 				"version": originalVersion,
 			},
 			bson.M{
@@ -154,8 +161,8 @@ func (s *EventStore) Save(ctx context.Context, events []eh.Event, originalVersio
 			},
 		); err != nil {
 			return eh.EventStoreError{
-				BaseErr:   err,
 				Err:       ErrCouldNotSaveAggregate,
+				BaseErr:   err,
 				Namespace: eh.NamespaceFromContext(ctx),
 			}
 		}
@@ -166,16 +173,14 @@ func (s *EventStore) Save(ctx context.Context, events []eh.Event, originalVersio
 
 // Load implements the Load method of the eventhorizon.EventStore interface.
 func (s *EventStore) Load(ctx context.Context, id uuid.UUID) ([]eh.Event, error) {
-	sess := s.session.Copy()
-	defer sess.Close()
+	c := s.client.Database(s.dbName(ctx)).Collection("events")
 
 	var aggregate aggregateRecord
-	err := sess.DB(s.dbName(ctx)).C("events").FindId(id.String()).One(&aggregate)
-	if err == mgo.ErrNotFound {
+	err := c.FindOne(ctx, bson.M{"_id": id}).Decode(&aggregate)
+	if err == mongo.ErrNoDocuments {
 		return []eh.Event{}, nil
 	} else if err != nil {
 		return nil, eh.EventStoreError{
-			BaseErr:   err,
 			Err:       err,
 			Namespace: eh.NamespaceFromContext(ctx),
 		}
@@ -183,20 +188,24 @@ func (s *EventStore) Load(ctx context.Context, id uuid.UUID) ([]eh.Event, error)
 
 	events := make([]eh.Event, len(aggregate.Events))
 	for i, dbEvent := range aggregate.Events {
-		// Create an event of the correct type.
-		if data, err := eh.CreateEventData(dbEvent.EventType); err == nil {
-			// Manually decode the raw BSON event.
-			if err := dbEvent.RawData.Unmarshal(data); err != nil {
+		// Create an event of the correct type and decode from raw BSON.
+		if len(dbEvent.RawData) > 0 {
+			var err error
+			if dbEvent.data, err = eh.CreateEventData(dbEvent.EventType); err != nil {
 				return nil, eh.EventStoreError{
+					Err:       ErrCouldNotUnmarshalEvent,
 					BaseErr:   err,
+					Namespace: eh.NamespaceFromContext(ctx),
+				}
+			}
+			if err := bson.Unmarshal(dbEvent.RawData, dbEvent.data); err != nil {
+				return nil, eh.EventStoreError{
 					Err:       ErrCouldNotUnmarshalEvent,
+					BaseErr:   err,
 					Namespace: eh.NamespaceFromContext(ctx),
 				}
 			}
-
-			// Set conrcete event and zero out the decoded event.
-			dbEvent.data = data
-			dbEvent.RawData = bson.Raw{}
+			dbEvent.RawData = nil
 		}
 
 		events[i] = event{dbEvent: dbEvent}
@@ -207,46 +216,42 @@ func (s *EventStore) Load(ctx context.Context, id uuid.UUID) ([]eh.Event, error)
 
 // Replace implements the Replace method of the eventhorizon.EventStore interface.
 func (s *EventStore) Replace(ctx context.Context, event eh.Event) error {
-	sess := s.session.Copy()
-	defer sess.Close()
+	c := s.client.Database(s.dbName(ctx)).Collection("events")
 
 	// First check if the aggregate exists, the not found error in the update
 	// query can mean both that the aggregate or the event is not found.
-	n, err := sess.DB(s.dbName(ctx)).C("events").FindId(event.AggregateID().String()).Count()
-	if n == 0 {
+	if n, err := c.CountDocuments(ctx, bson.M{"_id": event.AggregateID()}); n == 0 {
 		return eh.ErrAggregateNotFound
 	} else if err != nil {
 		return eh.EventStoreError{
-			BaseErr:   err,
 			Err:       err,
 			Namespace: eh.NamespaceFromContext(ctx),
 		}
 	}
 
-	// Create the event record for the DB.
+	// Create the event record for the Database.
 	e, err := newDBEvent(ctx, event)
 	if err != nil {
 		return err
 	}
 
 	// Find and replace the event.
-	err = sess.DB(s.dbName(ctx)).C("events").Update(
+	if r, err := c.UpdateOne(ctx,
 		bson.M{
-			"_id":            event.AggregateID().String(),
+			"_id":            event.AggregateID(),
 			"events.version": event.Version(),
 		},
 		bson.M{
 			"$set": bson.M{"events.$": *e},
 		},
-	)
-	if err == mgo.ErrNotFound {
-		return eh.ErrInvalidEvent
-	} else if err != nil {
+	); err != nil {
 		return eh.EventStoreError{
-			BaseErr:   err,
 			Err:       ErrCouldNotSaveAggregate,
+			BaseErr:   err,
 			Namespace: eh.NamespaceFromContext(ctx),
 		}
+	} else if r.MatchedCount == 0 {
+		return eh.ErrInvalidEvent
 	}
 
 	return nil
@@ -254,12 +259,11 @@ func (s *EventStore) Replace(ctx context.Context, event eh.Event) error {
 
 // RenameEvent implements the RenameEvent method of the eventhorizon.EventStore interface.
 func (s *EventStore) RenameEvent(ctx context.Context, from, to eh.EventType) error {
-	sess := s.session.Copy()
-	defer sess.Close()
+	c := s.client.Database(s.dbName(ctx)).Collection("events")
 
 	// Find and rename all events.
 	// TODO: Maybe use change info.
-	if _, err := sess.DB(s.dbName(ctx)).C("events").UpdateAll(
+	if _, err := c.UpdateMany(ctx,
 		bson.M{
 			"events.event_type": string(from),
 		},
@@ -268,8 +272,8 @@ func (s *EventStore) RenameEvent(ctx context.Context, from, to eh.EventType) err
 		},
 	); err != nil {
 		return eh.EventStoreError{
-			BaseErr:   err,
 			Err:       ErrCouldNotSaveAggregate,
+			BaseErr:   err,
 			Namespace: eh.NamespaceFromContext(ctx),
 		}
 	}
@@ -279,31 +283,33 @@ func (s *EventStore) RenameEvent(ctx context.Context, from, to eh.EventType) err
 
 // Clear clears the event storage.
 func (s *EventStore) Clear(ctx context.Context) error {
-	if err := s.session.DB(s.dbName(ctx)).C("events").DropCollection(); err != nil {
+	c := s.client.Database(s.dbName(ctx)).Collection("events")
+
+	if err := c.Drop(ctx); err != nil {
 		return eh.EventStoreError{
-			BaseErr:   err,
 			Err:       ErrCouldNotClearDB,
+			BaseErr:   err,
 			Namespace: eh.NamespaceFromContext(ctx),
 		}
 	}
 	return nil
 }
 
-// Close closes the database session.
-func (s *EventStore) Close() {
-	s.session.Close()
+// Close closes the database client.
+func (s *EventStore) Close(ctx context.Context) {
+	s.client.Disconnect(ctx)
 }
 
-// dbName appends the namespace, if one is set, to the DB prefix to
-// get the name of the DB to use.
+// dbName appends the namespace, if one is set, to the Database prefix to
+// get the name of the Database to use.
 func (s *EventStore) dbName(ctx context.Context) string {
 	ns := eh.NamespaceFromContext(ctx)
 	return s.dbPrefix + "_" + ns
 }
 
-// aggregateRecord is the DB representation of an aggregate.
+// aggregateRecord is the Database representation of an aggregate.
 type aggregateRecord struct {
-	AggregateID string    `bson:"_id"`
+	AggregateID uuid.UUID `bson:"_id"`
 	Version     int       `bson:"version"`
 	Events      []dbEvent `bson:"events"`
 	// Type        string        `bson:"type"`
@@ -318,34 +324,34 @@ type dbEvent struct {
 	data          eh.EventData     `bson:"-"`
 	Timestamp     time.Time        `bson:"timestamp"`
 	AggregateType eh.AggregateType `bson:"aggregate_type"`
-	AggregateID   string           `bson:"_id"`
+	AggregateID   uuid.UUID        `bson:"_id"`
 	Version       int              `bson:"version"`
 }
 
 // newDBEvent returns a new dbEvent for an event.
 func newDBEvent(ctx context.Context, event eh.Event) (*dbEvent, error) {
+	e := &dbEvent{
+		EventType:     event.EventType(),
+		Timestamp:     event.Timestamp(),
+		AggregateType: event.AggregateType(),
+		AggregateID:   event.AggregateID(),
+		Version:       event.Version(),
+	}
+
 	// Marshal event data if there is any.
-	var rawData bson.Raw
 	if event.Data() != nil {
-		raw, err := bson.Marshal(event.Data())
+		var err error
+		e.RawData, err = bson.Marshal(event.Data())
 		if err != nil {
 			return nil, eh.EventStoreError{
-				BaseErr:   err,
 				Err:       ErrCouldNotMarshalEvent,
+				BaseErr:   err,
 				Namespace: eh.NamespaceFromContext(ctx),
 			}
 		}
-		rawData = bson.Raw{Kind: 3, Data: raw}
 	}
 
-	return &dbEvent{
-		EventType:     event.EventType(),
-		RawData:       rawData,
-		Timestamp:     event.Timestamp(),
-		AggregateType: event.AggregateType(),
-		AggregateID:   event.AggregateID().String(),
-		Version:       event.Version(),
-	}, nil
+	return e, nil
 }
 
 // event is the private implementation of the eventhorizon.Event interface
@@ -356,11 +362,7 @@ type event struct {
 
 // AggrgateID implements the AggrgateID method of the eventhorizon.Event interface.
 func (e event) AggregateID() uuid.UUID {
-	id, err := uuid.Parse(e.dbEvent.AggregateID)
-	if err != nil {
-		return uuid.Nil
-	}
-	return id
+	return e.dbEvent.AggregateID
 }
 
 // AggregateType implements the AggregateType method of the eventhorizon.Event interface.
diff --git a/eventstore/mongodb/eventstore_test.go b/eventstore/mongodb/eventstore_test.go
index 2c3c62e2..184992b7 100644
--- a/eventstore/mongodb/eventstore_test.go
+++ b/eventstore/mongodb/eventstore_test.go
@@ -24,13 +24,12 @@ import (
 )
 
 func TestEventStore(t *testing.T) {
-	// Local Mongo testing with Docker
+	// Use MongoDB in Docker with fallback to localhost.
 	url := os.Getenv("MONGO_HOST")
-
 	if url == "" {
-		// Default to localhost
 		url = "localhost:27017"
 	}
+	url = "mongodb://" + url
 
 	store, err := NewEventStore(url, "test")
 	if err != nil {
@@ -40,27 +39,20 @@ func TestEventStore(t *testing.T) {
 		t.Fatal("there should be a store")
 	}
 
-	ctx := eh.NewContextWithNamespace(context.Background(), "ns")
+	customNamespaceCtx := eh.NewContextWithNamespace(context.Background(), "ns")
 
-	defer store.Close()
+	defer store.Close(context.Background())
 	defer func() {
-		t.Log("clearing db")
 		if err = store.Clear(context.Background()); err != nil {
 			t.Fatal("there should be no error:", err)
 		}
-		if err = store.Clear(ctx); err != nil {
+		if err = store.Clear(customNamespaceCtx); err != nil {
 			t.Fatal("there should be no error:", err)
 		}
 	}()
 
-	// Run the actual test suite.
-
-	t.Log("event store with default namespace")
+	// Run the actual test suite, both for default and custom namespace.
 	eventstore.AcceptanceTest(t, context.Background(), store)
-
-	t.Log("event store with other namespace")
-	eventstore.AcceptanceTest(t, ctx, store)
-
-	t.Log("event store maintainer")
+	eventstore.AcceptanceTest(t, customNamespaceCtx, store)
 	eventstore.MaintainerAcceptanceTest(t, context.Background(), store)
 }
diff --git a/eventstore/trace/eventstore_test.go b/eventstore/trace/eventstore_test.go
index 603891f5..b5cebd63 100644
--- a/eventstore/trace/eventstore_test.go
+++ b/eventstore/trace/eventstore_test.go
@@ -33,7 +33,7 @@ func TestEventStore(t *testing.T) {
 		t.Fatal("there should be a store")
 	}
 
-	// Run the actual test suite.
+	// Run the actual test suite, with tracing enabled.
 	store.StartTracing()
 	savedEvents := eventstore.AcceptanceTest(t, context.Background(), store)
 	store.StopTracing()
@@ -61,7 +61,7 @@ func TestEventStore(t *testing.T) {
 
 	ctx := context.Background()
 
-	t.Log("save event, version 7")
+	// Save event, version 7.
 	timestamp := time.Date(2009, time.November, 10, 23, 0, 0, 0, time.UTC)
 	event7 := eh.NewEventForAggregate(mocks.EventType, &mocks.EventData{Content: "event1"},
 		timestamp, mocks.AggregateType, event1.AggregateID(), 7)
@@ -75,7 +75,7 @@ func TestEventStore(t *testing.T) {
 		t.Error("there should be no events traced:", trace)
 	}
 
-	t.Log("load events without tracing")
+	// Load events without tracing.
 	events, err := store.Load(ctx, event1.AggregateID())
 	if err != nil {
 		t.Error("there should be no error:", err)
diff --git a/examples/guestlist/mongodb/mongodb_test.go b/examples/guestlist/mongodb/mongodb_test.go
index 81ab1774..bbbaba70 100644
--- a/examples/guestlist/mongodb/mongodb_test.go
+++ b/examples/guestlist/mongodb/mongodb_test.go
@@ -34,13 +34,12 @@ import (
 )
 
 func Example() {
-	// Local Mongo testing with Docker
+	// Use MongoDB in Docker with fallback to localhost.
 	url := os.Getenv("MONGO_HOST")
-
 	if url == "" {
-		// Default to localhost
 		url = "localhost:27017"
 	}
+	url = "mongodb://" + url
 
 	// Create the event store.
 	eventStore, err := eventstore.NewEventStore(url, "demo")
diff --git a/examples/todomvc/handler.go b/examples/todomvc/handler.go
index 5ef05a54..e12d4f7c 100644
--- a/examples/todomvc/handler.go
+++ b/examples/todomvc/handler.go
@@ -62,13 +62,12 @@ func (l *Logger) HandleEvent(ctx context.Context, event eh.Event) error {
 // NewHandler sets up the full Event Horizon domain for the TodoMVC app and
 // returns a handler exposing some of the components.
 func NewHandler() (*Handler, error) {
-	// Local Mongo testing with Docker
+	// Use MongoDB in Docker with fallback to localhost.
 	dbURL := os.Getenv("MONGO_HOST")
-
 	if dbURL == "" {
-		// Default to localhost
 		dbURL = "localhost:27017"
 	}
+	dbURL = "mongodb://" + dbURL
 
 	// Create the event store.
 	eventStore, err := eventstore.NewEventStore(dbURL, "todomvc")
diff --git a/examples/todomvc/handler_test.go b/examples/todomvc/handler_test.go
index 87abede6..9bd381dd 100644
--- a/examples/todomvc/handler_test.go
+++ b/examples/todomvc/handler_test.go
@@ -201,8 +201,8 @@ func TestDelete(t *testing.T) {
 	defer cancel()
 	l.Wait(ctx)
 
-	if _, err := h.Repo.Find(context.Background(), id); err == nil ||
-		err.Error() != "could not find entity: not found (default)" {
+	_, err = h.Repo.Find(context.Background(), id)
+	if rrErr, ok := err.(eh.RepoError); !ok || rrErr.Err != eh.ErrEntityNotFound {
 		t.Error("there should be a not found error:", err)
 	}
 }
diff --git a/go.mod b/go.mod
index b82b6fb3..8ebb4cce 100644
--- a/go.mod
+++ b/go.mod
@@ -4,11 +4,11 @@ go 1.14
 
 require (
 	cloud.google.com/go/pubsub v1.3.1
-	github.com/globalsign/mgo v0.0.0-20181015135952-eeefdecb41b8
 	github.com/google/uuid v1.1.1
 	github.com/gorhill/cronexpr v0.0.0-20180427100037-88b0669f7d75
 	github.com/gorilla/websocket v1.4.2
 	github.com/jpillora/backoff v1.0.0
 	github.com/kr/pretty v0.2.0
+	go.mongodb.org/mongo-driver v1.3.1
 	google.golang.org/api v0.20.0
 )
diff --git a/go.sum b/go.sum
index 9876a4f8..789a0a3e 100644
--- a/go.sum
+++ b/go.sum
@@ -41,15 +41,41 @@ github.com/chzyer/test v0.0.0-20180213035817-a1ea475d72b1/go.mod h1:Q3SI9o4m/ZMn
 github.com/client9/misspell v0.3.4/go.mod h1:qj6jICC3Q7zFZvVWo7KLAzC3yx5G7kyvSDkc90ppPyw=
 github.com/cncf/udpa/go v0.0.0-20191209042840-269d4d468f6f/go.mod h1:M8M6+tZqaGXZJjfX53e64911xZQV5JYwmTeXPW+k8Sc=
 github.com/davecgh/go-spew v1.1.0/go.mod h1:J7Y8YcW2NihsgmVo/mv3lAwl/skON4iLHjSsI+c5H38=
+github.com/davecgh/go-spew v1.1.1 h1:vj9j/u1bqnvCEfJOwUhtlOARqs3+rkHYY13jYWTU97c=
+github.com/davecgh/go-spew v1.1.1/go.mod h1:J7Y8YcW2NihsgmVo/mv3lAwl/skON4iLHjSsI+c5H38=
 github.com/envoyproxy/go-control-plane v0.9.0/go.mod h1:YTl/9mNaCwkRvm6d1a2C3ymFceY/DCBVvsKhRF0iEA4=
 github.com/envoyproxy/go-control-plane v0.9.1-0.20191026205805-5f8ba28d4473/go.mod h1:YTl/9mNaCwkRvm6d1a2C3ymFceY/DCBVvsKhRF0iEA4=
 github.com/envoyproxy/go-control-plane v0.9.4/go.mod h1:6rpuAdCZL397s3pYoYcLgu1mIlRU8Am5FuJP05cCM98=
 github.com/envoyproxy/protoc-gen-validate v0.1.0/go.mod h1:iSmxcyjqTsJpI2R4NaDN7+kN2VEUnK/pcBlmesArF7c=
-github.com/globalsign/mgo v0.0.0-20181015135952-eeefdecb41b8 h1:DujepqpGd1hyOd7aW59XpK7Qymp8iy83xq74fLr21is=
-github.com/globalsign/mgo v0.0.0-20181015135952-eeefdecb41b8/go.mod h1:xkRDCp4j0OGD1HRkm4kmhM+pmpv3AKq5SU7GMg4oO/Q=
 github.com/go-gl/glfw v0.0.0-20190409004039-e6da0acd62b1/go.mod h1:vR7hzQXu2zJy9AVAgeJqvqgH9Q5CA+iKCZ2gyEVpxRU=
 github.com/go-gl/glfw/v3.3/glfw v0.0.0-20191125211704-12ad95a8df72/go.mod h1:tQ2UAYgL5IevRw8kRxooKSPJfGvJ9fJQFa0TUsXzTg8=
 github.com/go-gl/glfw/v3.3/glfw v0.0.0-20200222043503-6f7a984d4dc4/go.mod h1:tQ2UAYgL5IevRw8kRxooKSPJfGvJ9fJQFa0TUsXzTg8=
+github.com/go-stack/stack v1.8.0 h1:5SgMzNM5HxrEjV0ww2lTmX6E2Izsfxas4+YHWRs3Lsk=
+github.com/go-stack/stack v1.8.0/go.mod h1:v0f6uXyyMGvRgIKkXu+yp6POWl0qKG85gN/melR3HDY=
+github.com/gobuffalo/attrs v0.0.0-20190224210810-a9411de4debd/go.mod h1:4duuawTqi2wkkpB4ePgWMaai6/Kc6WEz83bhFwpHzj0=
+github.com/gobuffalo/depgen v0.0.0-20190329151759-d478694a28d3/go.mod h1:3STtPUQYuzV0gBVOY3vy6CfMm/ljR4pABfrTeHNLHUY=
+github.com/gobuffalo/depgen v0.1.0/go.mod h1:+ifsuy7fhi15RWncXQQKjWS9JPkdah5sZvtHc2RXGlg=
+github.com/gobuffalo/envy v1.6.15/go.mod h1:n7DRkBerg/aorDM8kbduw5dN3oXGswK5liaSCx4T5NI=
+github.com/gobuffalo/envy v1.7.0/go.mod h1:n7DRkBerg/aorDM8kbduw5dN3oXGswK5liaSCx4T5NI=
+github.com/gobuffalo/flect v0.1.0/go.mod h1:d2ehjJqGOH/Kjqcoz+F7jHTBbmDb38yXA598Hb50EGs=
+github.com/gobuffalo/flect v0.1.1/go.mod h1:8JCgGVbRjJhVgD6399mQr4fx5rRfGKVzFjbj6RE/9UI=
+github.com/gobuffalo/flect v0.1.3/go.mod h1:8JCgGVbRjJhVgD6399mQr4fx5rRfGKVzFjbj6RE/9UI=
+github.com/gobuffalo/genny v0.0.0-20190329151137-27723ad26ef9/go.mod h1:rWs4Z12d1Zbf19rlsn0nurr75KqhYp52EAGGxTbBhNk=
+github.com/gobuffalo/genny v0.0.0-20190403191548-3ca520ef0d9e/go.mod h1:80lIj3kVJWwOrXWWMRzzdhW3DsrdjILVil/SFKBzF28=
+github.com/gobuffalo/genny v0.1.0/go.mod h1:XidbUqzak3lHdS//TPu2OgiFB+51Ur5f7CSnXZ/JDvo=
+github.com/gobuffalo/genny v0.1.1/go.mod h1:5TExbEyY48pfunL4QSXxlDOmdsD44RRq4mVZ0Ex28Xk=
+github.com/gobuffalo/gitgen v0.0.0-20190315122116-cc086187d211/go.mod h1:vEHJk/E9DmhejeLeNt7UVvlSGv3ziL+djtTr3yyzcOw=
+github.com/gobuffalo/gogen v0.0.0-20190315121717-8f38393713f5/go.mod h1:V9QVDIxsgKNZs6L2IYiGR8datgMhB577vzTDqypH360=
+github.com/gobuffalo/gogen v0.1.0/go.mod h1:8NTelM5qd8RZ15VjQTFkAW6qOMx5wBbW4dSCS3BY8gg=
+github.com/gobuffalo/gogen v0.1.1/go.mod h1:y8iBtmHmGc4qa3urIyo1shvOD8JftTtfcKi+71xfDNE=
+github.com/gobuffalo/logger v0.0.0-20190315122211-86e12af44bc2/go.mod h1:QdxcLw541hSGtBnhUc4gaNIXRjiDppFGaDqzbrBd3v8=
+github.com/gobuffalo/mapi v1.0.1/go.mod h1:4VAGh89y6rVOvm5A8fKFxYG+wIW6LO1FMTG9hnKStFc=
+github.com/gobuffalo/mapi v1.0.2/go.mod h1:4VAGh89y6rVOvm5A8fKFxYG+wIW6LO1FMTG9hnKStFc=
+github.com/gobuffalo/packd v0.0.0-20190315124812-a385830c7fc0/go.mod h1:M2Juc+hhDXf/PnmBANFCqx4DM3wRbgDvnVWeG2RIxq4=
+github.com/gobuffalo/packd v0.1.0/go.mod h1:M2Juc+hhDXf/PnmBANFCqx4DM3wRbgDvnVWeG2RIxq4=
+github.com/gobuffalo/packr/v2 v2.0.9/go.mod h1:emmyGweYTm6Kdper+iywB6YK5YzuKchGtJQZ0Odn4pQ=
+github.com/gobuffalo/packr/v2 v2.2.0/go.mod h1:CaAwI0GPIAv+5wKLtv8Afwl+Cm78K/I/VCm/3ptBN+0=
+github.com/gobuffalo/syncx v0.0.0-20190224160051-33c29581e754/go.mod h1:HhnNqWY95UYwwW3uSASeV7vtgYkT2t16hJgV3AEPUpw=
 github.com/golang/glog v0.0.0-20160126235308-23def4e6c14b h1:VKtxabqXZkF25pY9ekfRL6a582T4P37/31XEstQ5p58=
 github.com/golang/glog v0.0.0-20160126235308-23def4e6c14b/go.mod h1:SBH7ygxi8pfUlaOkMMuAQtPIUF8ecWP5IEl/CR7VP2Q=
 github.com/golang/groupcache v0.0.0-20190702054246-869f871628b6/go.mod h1:cIg4eruTrX1D+g88fzRXU5OdNfaM+9IcxsU14FzY7Hc=
@@ -68,6 +94,8 @@ github.com/golang/protobuf v1.3.2/go.mod h1:6lQm79b+lXiMfvg/cZm0SGofjICqVBUtrP5y
 github.com/golang/protobuf v1.3.3/go.mod h1:vzj43D7+SQXF/4pzW/hwtAqwc6iTitCiVSaWz5lYuqw=
 github.com/golang/protobuf v1.3.4 h1:87PNWwrRvUSnqS4dlcBU/ftvOIBep4sYuBLlh6rX2wk=
 github.com/golang/protobuf v1.3.4/go.mod h1:vzj43D7+SQXF/4pzW/hwtAqwc6iTitCiVSaWz5lYuqw=
+github.com/golang/snappy v0.0.1 h1:Qgr9rKW7uDUkrbSmQeiDsGa8SjGyCOGtuasMWwvp2P4=
+github.com/golang/snappy v0.0.1/go.mod h1:/XxbfmMg8lxefKM7IXC3fBNl/7bRcc72aCRzEWrmP2Q=
 github.com/google/btree v0.0.0-20180813153112-4030bb1f1f0c/go.mod h1:lNA+9X1NB3Zf8V7Ke586lFgjr2dZNuvo3lPJSGZ5JPQ=
 github.com/google/btree v1.0.0/go.mod h1:lNA+9X1NB3Zf8V7Ke586lFgjr2dZNuvo3lPJSGZ5JPQ=
 github.com/google/go-cmp v0.2.0 h1:+dTQ8DZQJz0Mb/HjFlkptS1FeQ4cWSnN941F8aEG4SQ=
@@ -96,12 +124,21 @@ github.com/gorilla/websocket v1.4.2/go.mod h1:YR8l580nyteQvAITg2hZ9XVh4b55+EU/ad
 github.com/hashicorp/golang-lru v0.5.0/go.mod h1:/m3WP610KZHVQ1SGc6re/UDhFvYD7pJ4Ao+sR/qLZy8=
 github.com/hashicorp/golang-lru v0.5.1/go.mod h1:/m3WP610KZHVQ1SGc6re/UDhFvYD7pJ4Ao+sR/qLZy8=
 github.com/ianlancetaylor/demangle v0.0.0-20181102032728-5e5cf60278f6/go.mod h1:aSSvb/t6k1mPoxDqO4vJh6VOCGPwU4O0C2/Eqndh1Sc=
+github.com/inconshreveable/mousetrap v1.0.0/go.mod h1:PxqpIevigyE2G7u3NXJIT2ANytuPF1OarO4DADm73n8=
+github.com/joho/godotenv v1.3.0/go.mod h1:7hK45KPybAkOC6peb+G5yklZfMxEjkZhHbwpqxOKXbg=
 github.com/jpillora/backoff v1.0.0 h1:uvFg412JmmHBHw7iwprIxkPMI+sGQ4kzOWsMeHnm2EA=
 github.com/jpillora/backoff v1.0.0/go.mod h1:J/6gKK9jxlEcS3zixgDgUAsiuZ7yrSoa/FX5e0EB2j4=
 github.com/jstemmer/go-junit-report v0.0.0-20190106144839-af01ea7f8024/go.mod h1:6v2b51hI/fHJwM22ozAgKL4VKDeJcHhJFhtBdhmNjmU=
 github.com/jstemmer/go-junit-report v0.9.1 h1:6QPYqodiu3GuPL+7mfx+NwDdp2eTkp9IfEUpgAwUN0o=
 github.com/jstemmer/go-junit-report v0.9.1/go.mod h1:Brl9GWCQeLvo8nXZwPNNblvFj/XSXhF0NWZEnDohbsk=
+github.com/karrick/godirwalk v1.8.0/go.mod h1:H5KPZjojv4lE+QYImBI8xVtrBRgYrIVsaRPx4tDPEn4=
+github.com/karrick/godirwalk v1.10.3/go.mod h1:RoGL9dQei4vP9ilrpETWE8CLOZ1kiN0LhBygSwrAsHA=
+github.com/kisielk/errcheck v1.2.0/go.mod h1:/BMXB+zMLi60iA8Vv6Ksmxu/1UDYcXs4uQLJ+jE2L00=
 github.com/kisielk/gotool v1.0.0/go.mod h1:XhKaO+MFFWcvkIS/tQcRk01m1F5IRFswLeQ+oQHNcck=
+github.com/klauspost/compress v1.9.5 h1:U+CaK85mrNNb4k8BNOfgJtJ/gr6kswUCFj6miSzVC6M=
+github.com/klauspost/compress v1.9.5/go.mod h1:RyIbtBH6LamlWaDj8nUwkbUhJ87Yi3uG0guNDohfE1A=
+github.com/konsorten/go-windows-terminal-sequences v1.0.1/go.mod h1:T0+1ngSBFLxvqU3pZ+m/2kptfBszLMUkC4ZK/EgS/cQ=
+github.com/konsorten/go-windows-terminal-sequences v1.0.2/go.mod h1:T0+1ngSBFLxvqU3pZ+m/2kptfBszLMUkC4ZK/EgS/cQ=
 github.com/kr/pretty v0.1.0 h1:L/CwN0zerZDmRFUapSPitk6f+Q3+0za1rQkzVuMiMFI=
 github.com/kr/pretty v0.1.0/go.mod h1:dAy3ld7l9f0ibDNOQOHHMYYIIbhfbHSm3C4ZsoJORNo=
 github.com/kr/pretty v0.2.0 h1:s5hAObm+yFO5uHYt5dYjxi2rXrsnmRpJx4OYvIWUaQs=
@@ -109,19 +146,50 @@ github.com/kr/pretty v0.2.0/go.mod h1:ipq/a2n7PKx3OHsz4KJII5eveXtPO4qwEXGdVfWzfn
 github.com/kr/pty v1.1.1/go.mod h1:pFQYn66WHrOpPYNljwOMqo10TkYh1fy3cYio2l3bCsQ=
 github.com/kr/text v0.1.0 h1:45sCR5RtlFHMR4UwH9sdQ5TC8v0qDQCHnXt+kaKSTVE=
 github.com/kr/text v0.1.0/go.mod h1:4Jbv+DJW3UT/LiOwJeYQe1efqtUx/iVham/4vfdArNI=
+github.com/markbates/oncer v0.0.0-20181203154359-bf2de49a0be2/go.mod h1:Ld9puTsIW75CHf65OeIOkyKbteujpZVXDpWK6YGZbxE=
+github.com/markbates/safe v1.0.1/go.mod h1:nAqgmRi7cY2nqMc92/bSEeQA+R4OheNU2T1kNSCBdG0=
+github.com/montanaflynn/stats v0.0.0-20171201202039-1bf9dbcd8cbe/go.mod h1:wL8QJuTMNUDYhXwkmfOly8iTdp5TEcJFWZD2D7SIkUc=
+github.com/pelletier/go-toml v1.4.0/go.mod h1:PN7xzY2wHTK0K9p34ErDQMlFxa51Fk0OUruD3k1mMwo=
+github.com/pkg/errors v0.8.0/go.mod h1:bwawxfHBFNV+L2hUp1rHADufV3IMtnDRdf1r5NINEl0=
+github.com/pkg/errors v0.8.1 h1:iURUrRGxPUNPdy5/HRSm+Yj6okJ6UtLINN0Q9M4+h3I=
+github.com/pkg/errors v0.8.1/go.mod h1:bwawxfHBFNV+L2hUp1rHADufV3IMtnDRdf1r5NINEl0=
+github.com/pmezard/go-difflib v1.0.0 h1:4DBwDE0NGyQoBHbLQYPwSUPoCMWR5BEzIk/f1lZbAQM=
 github.com/pmezard/go-difflib v1.0.0/go.mod h1:iKH77koFhYxTK1pcRnkKkqfTogsbg7gZNVY4sRDYZ/4=
 github.com/prometheus/client_model v0.0.0-20190812154241-14fe0d1b01d4/go.mod h1:xMI15A0UPsDsEKsMN9yxemIoYk6Tm2C1GtYGdfGttqA=
+github.com/rogpeppe/go-internal v1.1.0/go.mod h1:M8bDsm7K2OlrFYOpmOWEs/qY81heoFRclV5y23lUDJ4=
+github.com/rogpeppe/go-internal v1.2.2/go.mod h1:M8bDsm7K2OlrFYOpmOWEs/qY81heoFRclV5y23lUDJ4=
 github.com/rogpeppe/go-internal v1.3.0/go.mod h1:M8bDsm7K2OlrFYOpmOWEs/qY81heoFRclV5y23lUDJ4=
+github.com/sirupsen/logrus v1.4.0/go.mod h1:LxeOpSwHxABJmUn/MG1IvRgCAasNZTLOkJPxbbu5VWo=
+github.com/sirupsen/logrus v1.4.1/go.mod h1:ni0Sbl8bgC9z8RoU9G6nDWqqs/fq4eDPysMBDgk/93Q=
+github.com/sirupsen/logrus v1.4.2/go.mod h1:tLMulIdttU9McNUspp0xgXVQah82FyeX6MwdIuYE2rE=
+github.com/spf13/cobra v0.0.3/go.mod h1:1l0Ry5zgKvJasoi3XT1TypsSe7PqH0Sj9dhYf7v3XqQ=
+github.com/spf13/pflag v1.0.3/go.mod h1:DYY7MBk1bdzusC3SYhjObp+wFpr4gzcvqqNjLnInEg4=
 github.com/stretchr/objx v0.1.0/go.mod h1:HFkY916IF+rwdDfMAkV7OtwuqBVzrE8GR6GFx+wExME=
+github.com/stretchr/objx v0.1.1/go.mod h1:HFkY916IF+rwdDfMAkV7OtwuqBVzrE8GR6GFx+wExME=
+github.com/stretchr/testify v1.2.2/go.mod h1:a8OnRcib4nhh0OaRAV+Yts87kKdq0PP7pXfy6kDkUVs=
+github.com/stretchr/testify v1.3.0/go.mod h1:M5WIy9Dh21IEIfnGCwXGc5bZfKNJtfHm1UVUgZn+9EI=
+github.com/stretchr/testify v1.4.0 h1:2E4SXV/wtOkTonXsotYi4li6zVWxYlZuYNCXe9XRJyk=
 github.com/stretchr/testify v1.4.0/go.mod h1:j7eGeouHqKxXV5pUuKE4zz7dFj8WfuZ+81PSLYec5m4=
+github.com/tidwall/pretty v1.0.0 h1:HsD+QiTn7sK6flMKIvNmpqz1qrpP3Ps6jOKIKMooyg4=
+github.com/tidwall/pretty v1.0.0/go.mod h1:XNkn88O1ChpSDQmQeStsy+sBenx6DDtFZJxhVysOjyk=
+github.com/xdg/scram v0.0.0-20180814205039-7eeb5667e42c h1:u40Z8hqBAAQyv+vATcGgV0YCnDjqSL7/q/JyPhhJSPk=
+github.com/xdg/scram v0.0.0-20180814205039-7eeb5667e42c/go.mod h1:lB8K/P019DLNhemzwFU4jHLhdvlE6uDZjXFejJXr49I=
+github.com/xdg/stringprep v0.0.0-20180714160509-73f8eece6fdc h1:n+nNi93yXLkJvKwXNP9d55HC7lGK4H/SRcwB5IaUZLo=
+github.com/xdg/stringprep v0.0.0-20180714160509-73f8eece6fdc/go.mod h1:Jhud4/sHMO4oL310DaZAKk9ZaJ08SJfe+sJh0HrGL1Y=
+go.mongodb.org/mongo-driver v1.3.1 h1:op56IfTQiaY2679w922KVWa3qcHdml2K/Io8ayAOUEQ=
+go.mongodb.org/mongo-driver v1.3.1/go.mod h1:MSWZXKOynuguX+JSvwP8i+58jYCXxbia8HS3gZBapIE=
 go.opencensus.io v0.21.0/go.mod h1:mSImk1erAIZhrmZN+AvHh14ztQfjbGwt4TtuofqLduU=
 go.opencensus.io v0.22.0/go.mod h1:+kGneAE2xo2IficOXnaByMWTGM9T73dGwxeWcUqIpI8=
 go.opencensus.io v0.22.2/go.mod h1:yxeiOL68Rb0Xd1ddK5vPZ/oVn4vY4Ynel7k9FzqtOIw=
 go.opencensus.io v0.22.3 h1:8sGtKOrtQqkN1bp2AtX+misvLIlOmsEsNd+9NIcPEm8=
 go.opencensus.io v0.22.3/go.mod h1:yxeiOL68Rb0Xd1ddK5vPZ/oVn4vY4Ynel7k9FzqtOIw=
+golang.org/x/crypto v0.0.0-20180904163835-0709b304e793/go.mod h1:6SG95UA2DQfeDnfUPMdvaQW0Q7yPrPDi9nlGo2tz2b4=
 golang.org/x/crypto v0.0.0-20190308221718-c2843e01d9a2/go.mod h1:djNgcEr1/C05ACkg1iLfiJU5Ep61QUkGW8qpdssI0+w=
+golang.org/x/crypto v0.0.0-20190422162423-af44ce270edf/go.mod h1:WFFai1msRO1wXaEeE5yQxYXgSfI8pQAWXbQop6sCtWE=
 golang.org/x/crypto v0.0.0-20190510104115-cbcb75029529/go.mod h1:yigFU9vqHzYiE8UmvKecakEJjdnWj3jj499lnFckfCI=
+golang.org/x/crypto v0.0.0-20190530122614-20be4c3c3ed5/go.mod h1:yigFU9vqHzYiE8UmvKecakEJjdnWj3jj499lnFckfCI=
 golang.org/x/crypto v0.0.0-20190605123033-f99c8df09eb5/go.mod h1:yigFU9vqHzYiE8UmvKecakEJjdnWj3jj499lnFckfCI=
+golang.org/x/crypto v0.0.0-20191011191535-87dc89f01550 h1:ObdrDkeb4kJdCP557AjRjq69pTHfNouLtWZG7j9rPN8=
 golang.org/x/crypto v0.0.0-20191011191535-87dc89f01550/go.mod h1:yigFU9vqHzYiE8UmvKecakEJjdnWj3jj499lnFckfCI=
 golang.org/x/exp v0.0.0-20190121172915-509febef88a4/go.mod h1:CJ0aWSM057203Lf6IL+f9T1iT9GByDxfZKAQTCR3kQA=
 golang.org/x/exp v0.0.0-20190306152737-a1d7652674e8/go.mod h1:CJ0aWSM057203Lf6IL+f9T1iT9GByDxfZKAQTCR3kQA=
@@ -185,15 +253,21 @@ golang.org/x/sync v0.0.0-20180314180146-1d60e4601c6f/go.mod h1:RxMgew5VJxzue5/jJ
 golang.org/x/sync v0.0.0-20181108010431-42b317875d0f/go.mod h1:RxMgew5VJxzue5/jJTE5uejpjVlOe/izrB70Jof72aM=
 golang.org/x/sync v0.0.0-20181221193216-37e7f081c4d4/go.mod h1:RxMgew5VJxzue5/jJTE5uejpjVlOe/izrB70Jof72aM=
 golang.org/x/sync v0.0.0-20190227155943-e225da77a7e6/go.mod h1:RxMgew5VJxzue5/jJTE5uejpjVlOe/izrB70Jof72aM=
+golang.org/x/sync v0.0.0-20190412183630-56d357773e84/go.mod h1:RxMgew5VJxzue5/jJTE5uejpjVlOe/izrB70Jof72aM=
 golang.org/x/sync v0.0.0-20190423024810-112230192c58/go.mod h1:RxMgew5VJxzue5/jJTE5uejpjVlOe/izrB70Jof72aM=
 golang.org/x/sync v0.0.0-20190911185100-cd5d95a43a6e h1:vcxGaoTs7kV8m5Np9uUNQin4BrLOthgV7252N8V+FwY=
 golang.org/x/sync v0.0.0-20190911185100-cd5d95a43a6e/go.mod h1:RxMgew5VJxzue5/jJTE5uejpjVlOe/izrB70Jof72aM=
 golang.org/x/sys v0.0.0-20180830151530-49385e6e1522/go.mod h1:STP8DvDyc/dI5b8T5hshtkjS+E42TnysNCUPdjciGhY=
+golang.org/x/sys v0.0.0-20180905080454-ebe1bf3edb33/go.mod h1:STP8DvDyc/dI5b8T5hshtkjS+E42TnysNCUPdjciGhY=
 golang.org/x/sys v0.0.0-20190215142949-d0b11bdaac8a/go.mod h1:STP8DvDyc/dI5b8T5hshtkjS+E42TnysNCUPdjciGhY=
 golang.org/x/sys v0.0.0-20190312061237-fead79001313/go.mod h1:h1NjWce9XRLGQEsW7wpKNCjG9DtNlClVuFLEZdDNbEs=
+golang.org/x/sys v0.0.0-20190403152447-81d4e9dc473e/go.mod h1:h1NjWce9XRLGQEsW7wpKNCjG9DtNlClVuFLEZdDNbEs=
 golang.org/x/sys v0.0.0-20190412213103-97732733099d/go.mod h1:h1NjWce9XRLGQEsW7wpKNCjG9DtNlClVuFLEZdDNbEs=
+golang.org/x/sys v0.0.0-20190419153524-e8e3143a4f4a/go.mod h1:h1NjWce9XRLGQEsW7wpKNCjG9DtNlClVuFLEZdDNbEs=
+golang.org/x/sys v0.0.0-20190422165155-953cdadca894/go.mod h1:h1NjWce9XRLGQEsW7wpKNCjG9DtNlClVuFLEZdDNbEs=
 golang.org/x/sys v0.0.0-20190502145724-3ef323f4f1fd/go.mod h1:h1NjWce9XRLGQEsW7wpKNCjG9DtNlClVuFLEZdDNbEs=
 golang.org/x/sys v0.0.0-20190507160741-ecd444e8653b/go.mod h1:h1NjWce9XRLGQEsW7wpKNCjG9DtNlClVuFLEZdDNbEs=
+golang.org/x/sys v0.0.0-20190531175056-4c3a928424d2/go.mod h1:h1NjWce9XRLGQEsW7wpKNCjG9DtNlClVuFLEZdDNbEs=
 golang.org/x/sys v0.0.0-20190606165138-5da285871e9c/go.mod h1:h1NjWce9XRLGQEsW7wpKNCjG9DtNlClVuFLEZdDNbEs=
 golang.org/x/sys v0.0.0-20190624142023-c5567b49c5d0/go.mod h1:h1NjWce9XRLGQEsW7wpKNCjG9DtNlClVuFLEZdDNbEs=
 golang.org/x/sys v0.0.0-20190726091711-fc99dfbffb4e/go.mod h1:h1NjWce9XRLGQEsW7wpKNCjG9DtNlClVuFLEZdDNbEs=
@@ -217,14 +291,19 @@ golang.org/x/time v0.0.0-20181108054448-85acf8d2951c/go.mod h1:tRJNPiyCQ0inRvYxb
 golang.org/x/time v0.0.0-20190308202827-9d24e82272b4/go.mod h1:tRJNPiyCQ0inRvYxbN9jk5I+vvW/OXSQhTDSoE431IQ=
 golang.org/x/time v0.0.0-20191024005414-555d28b269f0/go.mod h1:tRJNPiyCQ0inRvYxbN9jk5I+vvW/OXSQhTDSoE431IQ=
 golang.org/x/tools v0.0.0-20180917221912-90fa682c2a6e/go.mod h1:n7NCudcB/nEzxVGmLbDWY5pfWTLqBcC2KZ6jyYvM4mQ=
+golang.org/x/tools v0.0.0-20181030221726-6c7e314b6563/go.mod h1:n7NCudcB/nEzxVGmLbDWY5pfWTLqBcC2KZ6jyYvM4mQ=
 golang.org/x/tools v0.0.0-20190114222345-bf090417da8b/go.mod h1:n7NCudcB/nEzxVGmLbDWY5pfWTLqBcC2KZ6jyYvM4mQ=
 golang.org/x/tools v0.0.0-20190226205152-f727befe758c/go.mod h1:9Yl7xja0Znq3iFh3HoIrodX9oNMXvdceNzlUR8zjMvY=
 golang.org/x/tools v0.0.0-20190311212946-11955173bddd/go.mod h1:LCzVGOaR6xXOjkQ3onu1FJEFr0SW1gC7cKk1uF8kGRs=
 golang.org/x/tools v0.0.0-20190312151545-0bb0c0a6e846/go.mod h1:LCzVGOaR6xXOjkQ3onu1FJEFr0SW1gC7cKk1uF8kGRs=
 golang.org/x/tools v0.0.0-20190312170243-e65039ee4138/go.mod h1:LCzVGOaR6xXOjkQ3onu1FJEFr0SW1gC7cKk1uF8kGRs=
+golang.org/x/tools v0.0.0-20190329151228-23e29df326fe/go.mod h1:LCzVGOaR6xXOjkQ3onu1FJEFr0SW1gC7cKk1uF8kGRs=
+golang.org/x/tools v0.0.0-20190416151739-9c9e1878f421/go.mod h1:LCzVGOaR6xXOjkQ3onu1FJEFr0SW1gC7cKk1uF8kGRs=
+golang.org/x/tools v0.0.0-20190420181800-aa740d480789/go.mod h1:LCzVGOaR6xXOjkQ3onu1FJEFr0SW1gC7cKk1uF8kGRs=
 golang.org/x/tools v0.0.0-20190425150028-36563e24a262/go.mod h1:RgjU9mgBXZiqYHBnxXauZ1Gv1EHHAz9KjViQ78xBX0Q=
 golang.org/x/tools v0.0.0-20190506145303-2d16b83fe98c/go.mod h1:RgjU9mgBXZiqYHBnxXauZ1Gv1EHHAz9KjViQ78xBX0Q=
 golang.org/x/tools v0.0.0-20190524140312-2c0ae7006135/go.mod h1:RgjU9mgBXZiqYHBnxXauZ1Gv1EHHAz9KjViQ78xBX0Q=
+golang.org/x/tools v0.0.0-20190531172133-b3315ee88b7d/go.mod h1:/rFqwRUd4F7ZHNgwSSTFct+R/Kf4OFW1sUzUTQQTgfc=
 golang.org/x/tools v0.0.0-20190606124116-d0a3d012864b/go.mod h1:/rFqwRUd4F7ZHNgwSSTFct+R/Kf4OFW1sUzUTQQTgfc=
 golang.org/x/tools v0.0.0-20190621195816-6e04913cbbac/go.mod h1:/rFqwRUd4F7ZHNgwSSTFct+R/Kf4OFW1sUzUTQQTgfc=
 golang.org/x/tools v0.0.0-20190628153133-6cdbf07be9d0/go.mod h1:/rFqwRUd4F7ZHNgwSSTFct+R/Kf4OFW1sUzUTQQTgfc=
@@ -307,6 +386,7 @@ gopkg.in/check.v1 v0.0.0-20161208181325-20d25e280405/go.mod h1:Co6ibVJAznAaIkqp8
 gopkg.in/check.v1 v1.0.0-20180628173108-788fd7840127 h1:qIbj1fsPNlZgppZ+VLlY7N33q108Sa+fhmuc+sWQYwY=
 gopkg.in/check.v1 v1.0.0-20180628173108-788fd7840127/go.mod h1:Co6ibVJAznAaIkqp8huTwlJQCZ016jof/cbN4VW5Yz0=
 gopkg.in/errgo.v2 v2.1.0/go.mod h1:hNsd1EY+bozCKY1Ytp96fpM3vjJbqLJn88ws8XvfDNI=
+gopkg.in/yaml.v2 v2.2.2 h1:ZCJp+EgiOT7lHqUV2J862kp8Qj64Jo6az82+3Td9dZw=
 gopkg.in/yaml.v2 v2.2.2/go.mod h1:hI93XBmqTisBFMUTm0b8Fm+jr3Dg1NNxqwp+5A1VGuI=
 honnef.co/go/tools v0.0.0-20190102054323-c2f93a96b099/go.mod h1:rf3lG4BRIbNafJWhAfAdb/ePZxsR/4RtNHQocxwk9r4=
 honnef.co/go/tools v0.0.0-20190106161140-3f1c8253044a/go.mod h1:rf3lG4BRIbNafJWhAfAdb/ePZxsR/4RtNHQocxwk9r4=
diff --git a/repo.go b/repo.go
index d609b943..cf7cac91 100644
--- a/repo.go
+++ b/repo.go
@@ -95,8 +95,8 @@ type Versionable interface {
 // from repos that support it. You must call Close() on each Iter even when
 // results were delivered without apparent error.
 type Iter interface {
-	Next() bool
+	Next(context.Context) bool
 	Value() interface{}
 	// Close must be called after the last Next() to retrieve error if any
-	Close() error
+	Close(context.Context) error
 }
diff --git a/repo/mongodb/repo.go b/repo/mongodb/repo.go
index 1d4c4687..3ff5dea6 100644
--- a/repo/mongodb/repo.go
+++ b/repo/mongodb/repo.go
@@ -18,8 +18,16 @@ import (
 	"context"
 	"errors"
 
-	"github.com/globalsign/mgo"
 	"github.com/google/uuid"
+	"go.mongodb.org/mongo-driver/bson"
+	"go.mongodb.org/mongo-driver/mongo"
+	"go.mongodb.org/mongo-driver/mongo/options"
+	"go.mongodb.org/mongo-driver/mongo/readconcern"
+	"go.mongodb.org/mongo-driver/mongo/readpref"
+	"go.mongodb.org/mongo-driver/mongo/writeconcern"
+
+	// Register uuid.UUID as BSON type.
+	_ "github.com/looplab/eventhorizon/types/mongodb"
 
 	eh "github.com/looplab/eventhorizon"
 )
@@ -27,8 +35,8 @@ import (
 // ErrCouldNotDialDB is when the database could not be dialed.
 var ErrCouldNotDialDB = errors.New("could not dial database")
 
-// ErrNoDBSession is when no database session is set.
-var ErrNoDBSession = errors.New("no database session")
+// ErrNoDBClient is when no database client is set.
+var ErrNoDBClient = errors.New("no database client")
 
 // ErrCouldNotClearDB is when the database could not be cleared.
 var ErrCouldNotClearDB = errors.New("could not clear database")
@@ -41,33 +49,34 @@ var ErrInvalidQuery = errors.New("invalid query")
 
 // Repo implements an MongoDB repository for entities.
 type Repo struct {
-	session    *mgo.Session
+	client     *mongo.Client
 	dbPrefix   string
 	collection string
 	factoryFn  func() eh.Entity
 }
 
 // NewRepo creates a new Repo.
-func NewRepo(url, dbPrefix, collection string) (*Repo, error) {
-	session, err := mgo.Dial(url)
+func NewRepo(uri, dbPrefix, collection string) (*Repo, error) {
+	opts := options.Client().ApplyURI(uri)
+	opts.SetWriteConcern(writeconcern.New(writeconcern.WMajority()))
+	opts.SetReadConcern(readconcern.Majority())
+	opts.SetReadPreference(readpref.Primary())
+	client, err := mongo.Connect(context.TODO(), opts)
 	if err != nil {
 		return nil, ErrCouldNotDialDB
 	}
 
-	session.SetMode(mgo.Strong, true)
-	session.SetSafe(&mgo.Safe{W: 1})
-
-	return NewRepoWithSession(session, dbPrefix, collection)
+	return NewRepoWithClient(client, dbPrefix, collection)
 }
 
-// NewRepoWithSession creates a new Repo with a session.
-func NewRepoWithSession(session *mgo.Session, dbPrefix, collection string) (*Repo, error) {
-	if session == nil {
-		return nil, ErrNoDBSession
+// NewRepoWithClient creates a new Repo with a client.
+func NewRepoWithClient(client *mongo.Client, dbPrefix, collection string) (*Repo, error) {
+	if client == nil {
+		return nil, ErrNoDBClient
 	}
 
 	r := &Repo{
-		session:    session,
+		client:     client,
 		dbPrefix:   dbPrefix,
 		collection: collection,
 	}
@@ -82,9 +91,6 @@ func (r *Repo) Parent() eh.ReadRepo {
 
 // Find implements the Find method of the eventhorizon.ReadRepo interface.
 func (r *Repo) Find(ctx context.Context, id uuid.UUID) (eh.Entity, error) {
-	sess := r.session.Copy()
-	defer sess.Close()
-
 	if r.factoryFn == nil {
 		return nil, eh.RepoError{
 			Err:       ErrModelNotSet,
@@ -92,14 +98,20 @@ func (r *Repo) Find(ctx context.Context, id uuid.UUID) (eh.Entity, error) {
 		}
 	}
 
+	c := r.client.Database(r.dbName(ctx)).Collection(r.collection)
+
 	entity := r.factoryFn()
-	err := sess.DB(r.dbName(ctx)).C(r.collection).FindId(id).One(entity)
-	if err != nil {
+	if err := c.FindOne(ctx, bson.M{"_id": id.String()}).Decode(entity); err == mongo.ErrNoDocuments {
 		return nil, eh.RepoError{
 			Err:       eh.ErrEntityNotFound,
 			BaseErr:   err,
 			Namespace: eh.NamespaceFromContext(ctx),
 		}
+	} else if err != nil {
+		return nil, eh.RepoError{
+			Err:       err,
+			Namespace: eh.NamespaceFromContext(ctx),
+		}
 	}
 
 	return entity, nil
@@ -107,9 +119,6 @@ func (r *Repo) Find(ctx context.Context, id uuid.UUID) (eh.Entity, error) {
 
 // FindAll implements the FindAll method of the eventhorizon.ReadRepo interface.
 func (r *Repo) FindAll(ctx context.Context) ([]eh.Entity, error) {
-	sess := r.session.Copy()
-	defer sess.Close()
-
 	if r.factoryFn == nil {
 		return nil, eh.RepoError{
 			Err:       ErrModelNotSet,
@@ -117,14 +126,29 @@ func (r *Repo) FindAll(ctx context.Context) ([]eh.Entity, error) {
 		}
 	}
 
-	iter := sess.DB(r.dbName(ctx)).C(r.collection).Find(nil).Iter()
+	c := r.client.Database(r.dbName(ctx)).Collection(r.collection)
+
+	cursor, err := c.Find(ctx, bson.M{})
+	if err != nil {
+		return nil, eh.RepoError{
+			Err:       err,
+			Namespace: eh.NamespaceFromContext(ctx),
+		}
+	}
+
 	result := []eh.Entity{}
-	entity := r.factoryFn()
-	for iter.Next(entity) {
+	for cursor.Next(ctx) {
+		entity := r.factoryFn()
+		if err := cursor.Decode(entity); err != nil {
+			return nil, eh.RepoError{
+				Err:       err,
+				Namespace: eh.NamespaceFromContext(ctx),
+			}
+		}
 		result = append(result, entity)
-		entity = r.factoryFn()
 	}
-	if err := iter.Close(); err != nil {
+
+	if err := cursor.Close(ctx); err != nil {
 		return nil, eh.RepoError{
 			Err:       err,
 			Namespace: eh.NamespaceFromContext(ctx),
@@ -136,33 +160,36 @@ func (r *Repo) FindAll(ctx context.Context) ([]eh.Entity, error) {
 
 // The iterator is not thread safe.
 type iter struct {
-	session   *mgo.Session
-	iter      *mgo.Iter
+	cursor    *mongo.Cursor
 	data      eh.Entity
 	factoryFn func() eh.Entity
+	decodeErr error
 }
 
-func (i *iter) Next() bool {
+func (i *iter) Next(ctx context.Context) bool {
+	if !i.cursor.Next(ctx) {
+		return false
+	}
+
 	item := i.factoryFn()
-	more := i.iter.Next(item)
+	i.decodeErr = i.cursor.Decode(item)
 	i.data = item
-	return more
+	return true
 }
 
 func (i *iter) Value() interface{} {
 	return i.data
 }
 
-func (i *iter) Close() error {
-	err := i.iter.Close()
-	i.session.Close()
-	return err
+func (i *iter) Close(ctx context.Context) error {
+	if err := i.cursor.Close(ctx); err != nil {
+		return err
+	}
+	return i.decodeErr
 }
 
 // FindCustomIter returns a mgo cursor you can use to stream results of very large datasets
-func (r *Repo) FindCustomIter(ctx context.Context, callback func(*mgo.Collection) *mgo.Query) (eh.Iter, error) {
-	sess := r.session.Copy()
-
+func (r *Repo) FindCustomIter(ctx context.Context, f func(context.Context, *mongo.Collection) (*mongo.Cursor, error)) (eh.Iter, error) {
 	if r.factoryFn == nil {
 		return nil, eh.RepoError{
 			Err:       ErrModelNotSet,
@@ -170,9 +197,17 @@ func (r *Repo) FindCustomIter(ctx context.Context, callback func(*mgo.Collection
 		}
 	}
 
-	collection := sess.DB(r.dbName(ctx)).C(r.collection)
-	query := callback(collection)
-	if query == nil {
+	c := r.client.Database(r.dbName(ctx)).Collection(r.collection)
+
+	cursor, err := f(ctx, c)
+	if err != nil {
+		return nil, eh.RepoError{
+			BaseErr:   err,
+			Err:       ErrInvalidQuery,
+			Namespace: eh.NamespaceFromContext(ctx),
+		}
+	}
+	if cursor == nil {
 		return nil, eh.RepoError{
 			Err:       ErrInvalidQuery,
 			Namespace: eh.NamespaceFromContext(ctx),
@@ -180,8 +215,7 @@ func (r *Repo) FindCustomIter(ctx context.Context, callback func(*mgo.Collection
 	}
 
 	return &iter{
-		session:   sess,
-		iter:      query.Iter(),
+		cursor:    cursor,
 		factoryFn: r.factoryFn,
 	}, nil
 }
@@ -191,10 +225,7 @@ func (r *Repo) FindCustomIter(ctx context.Context, callback func(*mgo.Collection
 // the query in the callback and returning nil to block a second execution of
 // the same query in FindCustom. Expect a ErrInvalidQuery if returning a nil
 // query from the callback.
-func (r *Repo) FindCustom(ctx context.Context, callback func(*mgo.Collection) *mgo.Query) ([]interface{}, error) {
-	sess := r.session.Copy()
-	defer sess.Close()
-
+func (r *Repo) FindCustom(ctx context.Context, f func(context.Context, *mongo.Collection) (*mongo.Cursor, error)) ([]interface{}, error) {
 	if r.factoryFn == nil {
 		return nil, eh.RepoError{
 			Err:       ErrModelNotSet,
@@ -202,23 +233,36 @@ func (r *Repo) FindCustom(ctx context.Context, callback func(*mgo.Collection) *m
 		}
 	}
 
-	collection := sess.DB(r.dbName(ctx)).C(r.collection)
-	query := callback(collection)
-	if query == nil {
+	c := r.client.Database(r.dbName(ctx)).Collection(r.collection)
+
+	cursor, err := f(ctx, c)
+	if err != nil {
+		return nil, eh.RepoError{
+			BaseErr:   err,
+			Err:       ErrInvalidQuery,
+			Namespace: eh.NamespaceFromContext(ctx),
+		}
+	}
+	if cursor == nil {
 		return nil, eh.RepoError{
 			Err:       ErrInvalidQuery,
 			Namespace: eh.NamespaceFromContext(ctx),
 		}
 	}
 
-	iter := query.Iter()
 	result := []interface{}{}
 	entity := r.factoryFn()
-	for iter.Next(entity) {
+	for cursor.Next(ctx) {
+		if err := cursor.Decode(entity); err != nil {
+			return nil, eh.RepoError{
+				Err:       err,
+				Namespace: eh.NamespaceFromContext(ctx),
+			}
+		}
 		result = append(result, entity)
 		entity = r.factoryFn()
 	}
-	if err := iter.Close(); err != nil {
+	if err := cursor.Close(ctx); err != nil {
 		return nil, eh.RepoError{
 			Err:       err,
 			Namespace: eh.NamespaceFromContext(ctx),
@@ -230,9 +274,6 @@ func (r *Repo) FindCustom(ctx context.Context, callback func(*mgo.Collection) *m
 
 // Save implements the Save method of the eventhorizon.WriteRepo interface.
 func (r *Repo) Save(ctx context.Context, entity eh.Entity) error {
-	sess := r.session.Copy()
-	defer sess.Close()
-
 	if entity.EntityID() == uuid.Nil {
 		return eh.RepoError{
 			Err:       eh.ErrCouldNotSaveEntity,
@@ -241,8 +282,17 @@ func (r *Repo) Save(ctx context.Context, entity eh.Entity) error {
 		}
 	}
 
-	if _, err := sess.DB(r.dbName(ctx)).C(r.collection).UpsertId(
-		entity.EntityID(), entity); err != nil {
+	c := r.client.Database(r.dbName(ctx)).Collection(r.collection)
+
+	if _, err := c.UpdateOne(ctx,
+		bson.M{
+			"_id": entity.EntityID().String(),
+		},
+		bson.M{
+			"$set": entity,
+		},
+		options.Update().SetUpsert(true),
+	); err != nil {
 		return eh.RepoError{
 			Err:       eh.ErrCouldNotSaveEntity,
 			BaseErr:   err,
@@ -254,14 +304,16 @@ func (r *Repo) Save(ctx context.Context, entity eh.Entity) error {
 
 // Remove implements the Remove method of the eventhorizon.WriteRepo interface.
 func (r *Repo) Remove(ctx context.Context, id uuid.UUID) error {
-	sess := r.session.Copy()
-	defer sess.Close()
+	c := r.client.Database(r.dbName(ctx)).Collection(r.collection)
 
-	err := sess.DB(r.dbName(ctx)).C(r.collection).RemoveId(id)
-	if err != nil {
+	if r, err := c.DeleteOne(ctx, bson.M{"_id": id.String()}); err != nil {
+		return eh.RepoError{
+			Err:       err,
+			Namespace: eh.NamespaceFromContext(ctx),
+		}
+	} else if r.DeletedCount == 0 {
 		return eh.RepoError{
 			Err:       eh.ErrEntityNotFound,
-			BaseErr:   err,
 			Namespace: eh.NamespaceFromContext(ctx),
 		}
 	}
@@ -270,12 +322,10 @@ func (r *Repo) Remove(ctx context.Context, id uuid.UUID) error {
 }
 
 // Collection lets the function do custom actions on the collection.
-func (r *Repo) Collection(ctx context.Context, f func(*mgo.Collection) error) error {
-	sess := r.session.Copy()
-	defer sess.Close()
+func (r *Repo) Collection(ctx context.Context, f func(context.Context, *mongo.Collection) error) error {
+	c := r.client.Database(r.dbName(ctx)).Collection(r.collection)
 
-	c := sess.DB(r.dbName(ctx)).C(r.collection)
-	if err := f(c); err != nil {
+	if err := f(ctx, c); err != nil {
 		return eh.RepoError{
 			Err:       err,
 			Namespace: eh.NamespaceFromContext(ctx),
@@ -292,7 +342,9 @@ func (r *Repo) SetEntityFactory(f func() eh.Entity) {
 
 // Clear clears the read model database.
 func (r *Repo) Clear(ctx context.Context) error {
-	if err := r.session.DB(r.dbName(ctx)).C(r.collection).DropCollection(); err != nil {
+	c := r.client.Database(r.dbName(ctx)).Collection(r.collection)
+
+	if err := c.Drop(ctx); err != nil {
 		return eh.RepoError{
 			Err:       ErrCouldNotClearDB,
 			BaseErr:   err,
@@ -303,8 +355,8 @@ func (r *Repo) Clear(ctx context.Context) error {
 }
 
 // Close closes a database session.
-func (r *Repo) Close() {
-	r.session.Close()
+func (r *Repo) Close(ctx context.Context) {
+	r.client.Disconnect(ctx)
 }
 
 // dbName appends the namespace, if one is set, to the DB prefix to
diff --git a/repo/mongodb/repo_test.go b/repo/mongodb/repo_test.go
index 5d3ef616..8924b2cd 100644
--- a/repo/mongodb/repo_test.go
+++ b/repo/mongodb/repo_test.go
@@ -21,9 +21,9 @@ import (
 	"testing"
 	"time"
 
-	"github.com/globalsign/mgo"
-	"github.com/globalsign/mgo/bson"
 	"github.com/google/uuid"
+	"go.mongodb.org/mongo-driver/bson"
+	"go.mongodb.org/mongo-driver/mongo"
 
 	eh "github.com/looplab/eventhorizon"
 	"github.com/looplab/eventhorizon/mocks"
@@ -38,6 +38,7 @@ func TestReadRepo(t *testing.T) {
 		// Default to localhost
 		url = "localhost:27017"
 	}
+	url = "mongodb://" + url
 
 	r, err := NewRepo(url, "test", "mocks.Model")
 	if err != nil {
@@ -46,7 +47,7 @@ func TestReadRepo(t *testing.T) {
 	if r == nil {
 		t.Error("there should be a repository")
 	}
-	defer r.Close()
+
 	r.SetEntityFactory(func() eh.Entity {
 		return &mocks.Model{}
 	})
@@ -54,26 +55,22 @@ func TestReadRepo(t *testing.T) {
 		t.Error("the parent repo should be nil")
 	}
 
-	// Repo with default namespace.
+	customNamespaceCtx := eh.NewContextWithNamespace(context.Background(), "ns")
+
+	defer r.Close(context.Background())
 	defer func() {
-		t.Log("clearing default db")
 		if err = r.Clear(context.Background()); err != nil {
 			t.Fatal("there should be no error:", err)
 		}
-	}()
-	repo.AcceptanceTest(t, context.Background(), r)
-	extraRepoTests(t, context.Background(), r)
-
-	// Repo with other namespace.
-	ctx := eh.NewContextWithNamespace(context.Background(), "ns")
-	defer func() {
-		t.Log("clearing ns db")
-		if err = r.Clear(ctx); err != nil {
+		if err = r.Clear(customNamespaceCtx); err != nil {
 			t.Fatal("there should be no error:", err)
 		}
 	}()
-	repo.AcceptanceTest(t, ctx, r)
-	extraRepoTests(t, ctx, r)
+
+	repo.AcceptanceTest(t, context.Background(), r)
+	extraRepoTests(t, context.Background(), r)
+	repo.AcceptanceTest(t, customNamespaceCtx, r)
+	extraRepoTests(t, customNamespaceCtx, r)
 
 }
 
@@ -89,8 +86,8 @@ func extraRepoTests(t *testing.T, ctx context.Context, r *Repo) {
 	}
 
 	// FindCustom by content.
-	result, err := r.FindCustom(ctx, func(c *mgo.Collection) *mgo.Query {
-		return c.Find(bson.M{"content": "modelCustom"})
+	result, err := r.FindCustom(ctx, func(ctx context.Context, c *mongo.Collection) (*mongo.Cursor, error) {
+		return c.Find(ctx, bson.M{"content": "modelCustom"})
 	})
 	if len(result) != 1 {
 		t.Error("there should be one item:", len(result))
@@ -100,22 +97,22 @@ func extraRepoTests(t *testing.T, ctx context.Context, r *Repo) {
 	}
 
 	// FindCustom with no query.
-	result, err = r.FindCustom(ctx, func(c *mgo.Collection) *mgo.Query {
-		return nil
+	result, err = r.FindCustom(ctx, func(ctx context.Context, c *mongo.Collection) (*mongo.Cursor, error) {
+		return nil, nil
 	})
 	if rrErr, ok := err.(eh.RepoError); !ok || rrErr.Err != ErrInvalidQuery {
 		t.Error("there should be a invalid query error:", err)
 	}
 
-	count := 0
+	var count int64
 	// FindCustom with query execution in the callback.
-	_, err = r.FindCustom(ctx, func(c *mgo.Collection) *mgo.Query {
-		if count, err = c.Count(); err != nil {
+	_, err = r.FindCustom(ctx, func(ctx context.Context, c *mongo.Collection) (*mongo.Cursor, error) {
+		if count, err = c.CountDocuments(ctx, bson.M{}); err != nil {
 			t.Error("there should be no error:", err)
 		}
 
 		// Be sure to return nil to not execute the query again in FindCustom.
-		return nil
+		return nil, nil
 	})
 	if rrErr, ok := err.(eh.RepoError); !ok || rrErr.Err != ErrInvalidQuery {
 		t.Error("there should be a invalid query error:", err)
@@ -128,8 +125,9 @@ func extraRepoTests(t *testing.T, ctx context.Context, r *Repo) {
 		ID:      uuid.New(),
 		Content: "modelCustom2",
 	}
-	if err := r.Collection(ctx, func(c *mgo.Collection) error {
-		return c.Insert(modelCustom2)
+	if err := r.Collection(ctx, func(ctx context.Context, c *mongo.Collection) error {
+		_, err := c.InsertOne(ctx, modelCustom2)
+		return err
 	}); err != nil {
 		t.Error("there should be no error:", err)
 	}
@@ -142,23 +140,23 @@ func extraRepoTests(t *testing.T, ctx context.Context, r *Repo) {
 	}
 
 	// FindCustomIter by content.
-	iter, err := r.FindCustomIter(ctx, func(c *mgo.Collection) *mgo.Query {
-		return c.Find(bson.M{"content": "modelCustom"})
+	iter, err := r.FindCustomIter(ctx, func(ctx context.Context, c *mongo.Collection) (*mongo.Cursor, error) {
+		return c.Find(ctx, bson.M{"content": "modelCustom"})
 	})
 	if err != nil {
 		t.Error("there should be no error:", err)
 	}
 
-	if iter.Next() != true {
+	if iter.Next(ctx) != true {
 		t.Error("the iterator should have results")
 	}
 	if !reflect.DeepEqual(iter.Value(), modelCustom) {
 		t.Error("the item should be correct:", modelCustom)
 	}
-	if iter.Next() == true {
+	if iter.Next(ctx) == true {
 		t.Error("the iterator should have no results")
 	}
-	err = iter.Close()
+	err = iter.Close(ctx)
 	if err != nil {
 		t.Error("there should be no error:", err)
 	}
@@ -177,17 +175,17 @@ func TestRepository(t *testing.T) {
 
 	// Local Mongo testing with Docker
 	url := os.Getenv("MONGO_HOST")
-
 	if url == "" {
 		// Default to localhost
 		url = "localhost:27017"
 	}
+	url = "mongodb://" + url
 
 	repo, err := NewRepo(url, "test", "mocks.Model")
 	if err != nil {
 		t.Error("there should be no error:", err)
 	}
-	defer repo.Close()
+	defer repo.Close(context.Background())
 
 	outer := &mocks.Repo{ParentRepo: repo}
 	if r := Repository(outer); r != repo {
diff --git a/types/mongodb/uuid.go b/types/mongodb/uuid.go
new file mode 100644
index 00000000..cdb10404
--- /dev/null
+++ b/types/mongodb/uuid.go
@@ -0,0 +1,76 @@
+package mongodb
+
+import (
+	"fmt"
+	"reflect"
+
+	"github.com/google/uuid"
+	"go.mongodb.org/mongo-driver/bson"
+	"go.mongodb.org/mongo-driver/bson/bsoncodec"
+	"go.mongodb.org/mongo-driver/bson/bsonrw"
+	"go.mongodb.org/mongo-driver/bson/bsontype"
+)
+
+// Update the default BSON registry to be able to handle UUID types as strings.
+func init() {
+	rb := bson.NewRegistryBuilder()
+	var id uuid.UUID
+	uuidType := reflect.TypeOf(id)
+
+	rb.RegisterTypeEncoder(uuidType, bsoncodec.ValueEncoderFunc(
+		func(ec bsoncodec.EncodeContext, vw bsonrw.ValueWriter, val reflect.Value) error {
+			if !val.IsValid() || val.Type() != uuidType || val.Len() != 16 {
+				return bsoncodec.ValueEncoderError{
+					Name:     "uuid.UUID",
+					Types:    []reflect.Type{uuidType},
+					Received: val,
+				}
+			}
+			b := make([]byte, 16)
+			v := reflect.ValueOf(b)
+			reflect.Copy(v, val)
+			id, err := uuid.FromBytes(v.Bytes())
+			if err != nil {
+				return fmt.Errorf("could not parse UUID bytes (%x): %w", v.Bytes(), err)
+			}
+			return vw.WriteString(id.String())
+		},
+	))
+
+	rb.RegisterTypeDecoder(uuidType, bsoncodec.ValueDecoderFunc(
+		func(dc bsoncodec.DecodeContext, vr bsonrw.ValueReader, val reflect.Value) error {
+			if !val.IsValid() || !val.CanSet() || val.Kind() != reflect.Array {
+				return bsoncodec.ValueDecoderError{
+					Name:     "uuid.UUID",
+					Kinds:    []reflect.Kind{reflect.Bool},
+					Received: val,
+				}
+			}
+
+			var s string
+			switch vr.Type() {
+			case bsontype.String:
+				var err error
+				if s, err = vr.ReadString(); err != nil {
+					return err
+				}
+			default:
+				return fmt.Errorf("received invalid BSON type to decode into UUID: %s", vr.Type())
+			}
+
+			id, err := uuid.Parse(s)
+			if err != nil {
+				return fmt.Errorf("could not parse UUID string: %s", s)
+			}
+			v := reflect.ValueOf(id)
+			if !v.IsValid() || v.Kind() != reflect.Array {
+				return fmt.Errorf("invalid kind of reflected UUID value: %s", v.Kind().String())
+			}
+			reflect.Copy(val, v)
+
+			return nil
+		},
+	))
+
+	bson.DefaultRegistry = rb.Build()
+}