The Christian Social Union of Bavaria is a Christian democratic political party in Germany. It operates exclusively in the state of Bavaria, while its sister party, the CDU, operates in the rest of the country. On the federal level, the CSU is often perceived as the more socially conservative of the two parties. At times, especially when the CDU showed weaknesses, there has been considerable tension up to threats to break up the cooperation. Most of the time, however, they work together very closely.
Franz Josef Strauß (1915–1988) is seen as having set the ideological basis of the party, although he was too young to be a founding leader of the party, which began as a continuation of the Weimar-era Bavarian People's Party and, to a lesser extent, of the Catholic Centre Party.
The CSU has led the Bavarian state government practically since it came into existence, and without the need for a coalition government for most of the time. This level of dominance is unique in post-war Germany. On the federal level, it forms a common fraction in the Bundestag (Federal Parliament) with the CDU. Edmund Stoiber took over the CSU chairmanship early in 1999. He ran for Chancellor in 2002, but lost. In 2003, the CSU was re-elected as the Bavarian government with an 2/3 majority (60.7% and 124 of 180 seats in the state diet). On 18 January 2007, Stoiber announced his decision to stand down from the posts of minister-president and CSU chairman by 30 September after having been under fire in his own party for weeks.
The CSU has a strong support throughout Bavaria, but on a municipal level the situation is more diverse, with independant voter groups heading many municipal administrations, especially in the rural parts; the two largest cities, Munich and Nuremberg, have elected mayors from the German SPD - on a statewide and federal level the CSU usually wins the plurality in both cities. On 28 September 2008, the CSU failed to gain a majority in the Bavaria state election for the first time in half a century and is forced to select a coalition partner, which currently is expected to be the FDP.
The CSU is a member of the European People's Party (EPP) and its European parliamentarians sit in the EPP-ED group. At the moment they have two ministers in Berlin: Michael Glos (Minister of Economics and Technology) and Horst Seehofer (Minister of Food, Agriculture and Consumer Protection).