This book is an in-depth guide to using Drupal's most important modules, written by the author of two of those modules. The modules described in the book are widely considered essential modules that will be installed on almost every site; they allow for a level of customization that is unparalleled in the market and are a key reason that Drupal is being chosen over its competition, such as Joomla and WordPress. In addition to being a CMS, Drupal is also a content management framework and provides robust APIs upon which developers can create new functionality. Drupal code is written by members of Drupal's robust open source community and is further extensible and customizable to fit your exact needs.