Public transportation in Berlin is excellent. The Berliner Verkehrsbetriebe GmbH - BVG - is the public local transportation network of Berlin. Within this local network, you may use any means of public transport: regional trains (RB), regional express trains (RE), city railway (S-Bahn), subway (U-Bahn), streetcars (Straßenbahn), and buses (Bus and Metro-Bus). You just buy one ticket from A to B, irrespective of the means of transportation and regardless of whether and how often you have to change in between (as long as you reach your destination by travelling in one direction).
Berlin and the surrounding areas are divided into three fare zones (A, B and C). Tickets are available for two fare zones (AB or BC) or the entire fare zone (ABC).
Timetables, routes and maps can be downloaded here (in English).