U5 or U-5 may refer to:
U5 is a line on the Berlin U-Bahn. It runs from Alexanderplatz in Mitte eastwards through Friedrichshain, Lichtenberg and Friedrichsfelde, surfaces in Biesdorf-Süd to pass Kaulsdorf and Hellersdorf above ground and finally reaches city limits at Hönow.
U5 at present only connects to other U-bahn lines at its Alexanderplatz terminus, although work is ongoing to extend it across central Berlin to Berlin Hauptbahnhof, providing further U-Bahn and S-Bahn interchanges.
Only in 1927 did construction start on Pre WWI era for a rapid transit line underneath Große Frankfurter Straße (the present-day Karl-Marx-Allee). The design was planned and led by Johannes Bousset. The first section between Alexanderplatz and Friedrichsfelde, then named line E, was inaugurated on 21 December 1930 (However, it is not shown on the Pharus-Plan 1930 map).
During the time when Berlin was divided, the U5 was the only line to fall entirely within East Berlin, and the only line to be actively extended by the East German authorities. Work on this extension was started in September 1969. On 6 June 1973, the first extension was opened, to Tierpark station, serving the Tierpark zoo.
The U5 is a line on the Frankfurt U-Bahn. At the time of the line's inauguration in 1974, it ran from the central railway station to the Konstablerwache and then continued along the Eckenheimer Landstrasse all the way up to Preungesheim. After Konstablerwache the line is running above the ground towards Preungesheim.