Vienna U-Bahn

The Vienna U-Bahn (an abbreviation of Untergrundbahn, or underground railway) is a rapid transit (metro) system consisting of five lines. It is the backbone of one of the best performing public transport systems worldwide according to UITP (International Association of Public Transport) in June 2009. More than 1.3 million passengers use the Vienna U-Bahn every day. The network is undergoing expansion and rolling stock renewal. Since 1969, 200 million euro have been invested annually into the extension of the Vienna U-Bahn.

The first section of the modern U-Bahn opened on 8 May 1976, but two of the lines extended and later designated as U-Bahn (U4, U6) date back to the Stadtbahn ("city railway") system, which first opened in 1898. Parts of both the U2 and U6 originate from premetro tunnels built to accommodate earlier tram lines. Only the U1 and U3 were built wholly as new subway lines.

Lines are designated merely by a number and the prefix "U" (for U-Bahn) and identified on station signage and related literature by a colour. There are currently five lines; U1, U2, U3, U4 and U6. There have been numerous suggestions for a line U5 but all these projects have been shelved. Stations are often named after streets, public spaces or districts, and in some special cases after prominent buildings at or near the station, although the official policy of the Wiener Linien states that they prefer not to name stations after buildings.

Ticketing for the network is integrated under the Wiener Linien umbrella brand with all means of public transport in Vienna, including trams and buses. Local tickets are valid on S-Bahn suburban rail services and other train services but these are operated by the state railway operator, ÖBB. Tickets are not valid on bus services operated by Vienna Airport Lines and the City Airport Train express train.