If you are having problems with embedded forms for linking tables between many to many relationships, try adding a primary key to the linking table. At first I was using a composite primary key on my linking table and trying to figure out how to get it to work properly with form embedding, but was unable to. So I added a primary key, dropped the composite primary key and everything works as expected. This works well for forms you plan on embedding, if you just want to save M:M relationships via admin double list please visit my post on the topic: http://melikedev.com/2009/12/09/symfony-w-doctrine-saving-many-to-many-mm-relationships/