U1 is a line on the Berlin U-Bahn, which is 8.8 kilometres (5.5 mi) long and has 13 stations. Its traditional line designation was BII. It runs east–west and its eastern terminus is Warschauer Straße S-Bahn station where it connects to the Schlesische Bahn. From there it runs through Kreuzberg via Gleisdreieck and Wittenbergplatz on to the Kurfürstendamm.

The Berlin U-Bahn is a rapid transit system in Berlin, the capital and largest city of Germany, and a major part of the city's public transport system. Together with the S-Bahn, a network of suburban train lines, and a tram network that operates mostly in the eastern parts of the city, it serves as the main means of transport in the capital.