The Party of European Socialists (PES) is a European political party comprising of thirty-three socialist, social democratic and labour parties from each European Union member state and Norway. PES forms a parliamentary group in the European Parliament, the Socialist Group, which is the second largest grouping with over 200 MEPs.

The Party was founded in 1992 and is led by Poul Nyrup Rasmussen MEP. However the history of the Socialist Group goes back to the beginning of the European Parliament in 1953. Until the 1999 European election it had been the largest group elected in Parliament. The group is currently led by Martin Schulz MEP.