The Social Democratic Party was founded in 1888. It was considered to be the main opposition to the Radicals in government and parliament. After the General Strike in 1918, proportional representation was introduced which helped the Social Democrats gain 41 seats in parliament.
After the strike the party took a softer line and in 1943 it became the strongest party in parliament, finally gaining a seat in the cabinet. A second seat followed in 1959.
In the 1980s the centre-left Social Democrats fell out of favour, but recovered to be the strongest party at the 1995 elections. Since the 1999 elections it has been battling with the Swiss People's Party for the top spot in the voter popularity stakes. In the 2003 elections the Social Democrats received 23.3 per cent of the votes, behind the People's Party's 26.6 per cent.
The Social Democratic Party suffered a setback in the 2007 elections, losing nearly three per cent of the vote.
It is still the second largerst group in parliament with 42 seats in the House of Representatives and nine seats in the Senate.
President: Christian Levrat, Member of the House of Representatives
Seats in the House of Representatives: 42
Seats in the Senate: 9
Cabinet Ministers: Micheline Calmy-Rey and Moritz Leuenberger