Drupal is 10 years old so started back in the dark ages of PHP 3. So it started almost completely procedural but large chunks now have been converted to OOP. D

Drupal is 10 years old so started back in the dark ages of PHP 3. So it started almost completely procedural but large chunks now have been converted to OOP. Drupal doesn't follow the MVC pattern but the somewhat less common PAC (Presentation-Abstraction-Control) pattern. See http://www.garfieldtech.com/blog/mvc-vs-pac http://www.garfieldtech.com/blog/mvc-vs-pac for a good overview of the differences between MVC and PAC and how Drupal implements it.