The Rails team is perpetually improving Rails and releasing new versions. This book was originally written using Rails 2.0 and 2.1, and all examples have been tested in 2.1 and 2.2. 2.3 will be out soon, and while it has more changes than 2.1 or 2.2, most of them don't look likely to affect the examples here. There are notes in a few places pointing out where things may look a little different in different versions. We’ll post updates in new versions of this electronic book and at http://www.excursionsonrails.com.