The first edition covers Drupal 5 (though much of the information applies to Drupal 6). The second edition covers Drupal 6.

Drupal is one of the most popular content management systems in use today. With it, you can create a variety of community-driven sites, including blogs, forums, wiki-style sites, and much more. Pro Drupal Development was written to arm you with knowledge to customize your Drupal installation however you see fit. Authors John VanDyk and Matt Westgate delve into Drupal internals, showing you how to truly take advantage of its powerful architecture.