The current edition of "The Rust Programming Language" is the second edition, which you can read here.
The source for all editions lives on GitHub. Please open issues with any questions, concerns, or tweaks.
The second edition is still receiving some minor edits, but is effectively complete. It will be available in dead-tree form through NoStarch Press once these final edits are complete.
The second edition is a complete re-write of TRPL, from the ground up, and is therefore very different from the first edition.
We keep older editions of TRPL online for history's sake.
You can read the first edition of "The Rust Programming Language" here.