Programmer's Guide to Drupal (repost)

If you’re a web programmer new to Drupal, this book shows you which programming techniques you can use—and which you should avoid—when building custom web applications with this content management framework.

Drupal has its own set of programming principles that require a different approach, and many programmers make mistakes when relying on skills they’ve used for other projects. The guidelines in this book help you through the transition by demonstrating which programming practices conform to the “Drupal way,” and which don’t.

If you’re familiar with PHP, you’ll quickly learn how to take advantage of the powerful Drupal API.
Get a complete overview of Drupal, including Drupal core and add-on modules and themes
Learn Drupal’s basic programming principles, such as the ability to customize behavior and output with hooks
Discover common Drupal programming mistakes—and why hacking is one of them
Explore specific areas where you can put your programming skills to work
Learn programming tips and tools to help you perfect and debug your applications