BVG (public transportation guide):

The public transportation network consists of underground metro, busses, trains (S-Bahn) and trams. When using a bus passengers have to enter at the front door and show their tickets to the bus driver. The penalty for not having a valid ticket is 60€. The Berlin tariff area is subdivided into zones A, B & C.

Please note: Beware of tricksters! Please buy your tickets only at official outlets.