The Party of Democratic Socialism (German: Partei des Demokratischen Sozialismus, PDS) was a democratic socialist political party in Germany active between 1989 and 2007. It was the legal successor to the Socialist Unity Party of Germany (SED), which ruled the German Democratic Republic (East Germany) as a state party until 1990. From 1990 through to 2005, the PDS had been seen as the left-wing "party of the East". While it achieved minimal support in western Germany, it regularly won 15% to 25% of the vote in the eastern new states of Germany, entering coalition governments (with the Social Democratic Party of Germany, SPD) in the federal states of Mecklenburg-Vorpommern and Berlin.

In 2005, the PDS, renamed The Left Party.PDS (Die Linkspartei.PDS) entered an electoral alliance with the Western Germany-based Electoral Alternative for Labour and Social Justice (WASG) and won 8.7% of the vote in Germany's September 2005 federal elections (more than double the 4% share achieved by the PDS alone in the 2002 federal election). On 16 June 2007, the two groupings merged to form a new party called The Left (Die Linke).

The party had many socially progressive policies, including support for legalisation of same-sex marriage and greater social welfare for immigrants.

Internationally, the Left Party.PDS was a co-founder of the Party of the European Left and was the largest party in the European United Left–Nordic Green Left (GUE/NGL) group in the European Parliament.