Doctrine2 is an ORM (Object relational mapper) library for PHP, and is one of the best things to happen to the PHP world, so far. The main point of an ORM is, to put it simply, to allow you to map PHP objects, to database tables. You can save and load your objects to/from the database, in a general way, that is, you don't need to write select/insert/update/delete SQL queries for them, because the ORM will take care of that for you.