Alliance of the Democratic Left (Polish: Sojusz Lewicy Demokratycznej, SLD) is the main Polish social democratic political party, established on April 15th, 1999.

Most of its members had previously been members of SdRP (Socjaldemokracja Rzeczypospolitej Polskiej - Socialdemocracy of the Republic of Poland). SdRP and some other socialist and social democratic parties formed a left-wing coalition called Sojusz Lewicy Demokratycznej (1991-1999). In 1999 the coalition became a party, but lost some members. That coalition was established mostly by former members of PZPR (Polska Zjednoczona Partia Robotnicza - Polish United Workers Party), which ruled in Poland until 1989. PZPR was a communist party, but today's SLD is a pro-European social democratic party. A coalition between SLD and PSL ruled Poland in the years 1993-1997.

The president of SLD is Leszek Miller, who has been Prime Minister of Poland since 2001. The former president of SLD, Aleksander Kwasniewski, became President of Poland in December 1995.

SLD has 200 (of 460) members of the Sejm (the lower house) and over 70 senators (of 100). In the 2001 election, SLD formed a coalition with Unia Pracy (UP, Labour Union). After the election, the coalition was joined by Polskie Stronnictwo Ludowe (the Polish Peasants' Party) in forming a government. In March 2003 PSL left the coalition.

Sojusz Lewicy Demokratycznej in the World Wide Web:

The coalition between SLD and UP: