Sixth Division

The Sixth Division (六番隊, rokubantai), also known as Squad 6 in the English dub, is one of the Gotei 13, headed by Captain Byakuya Kuchiki.
The sixth Division follows the traditional organization of a Gotei 13  Division.
No special duties have been noted for the 6th Division. The 6th Division is seen as a model division by every Shinigami and is known for its strict adherence to rules.
Like all the other barracks, the 6th Division Barracks house the offices and living quarters of the Shinigami of the 6th. Byakuya's office is notable for having shelves of books lining its walls.

Info from :  http://bleach.wikia.com/