Pro Drupal Development 2nd. Edition (August 2008)

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.
You'll learn how to write your own modules, create your own themes while adhering to best practices that keep your site easy to maintain.

You'll learn the inner workings of each key part of Drupal, including user management, sessions, the node system, caching, and the various APIs available to you. Of course, your Drupal-powered site isn't effective until you can efficiently serve pages to your visitors. As such, the authors have included the information you need to optimize your Drupal installation to perform well under high-load situations. Also featured is information on Drupal security and integration of Ajax and the internationalization of your Drupal web site. Simply put, if you are working with Drupal at all, then you need this book!