transnational parliamentary group representing the interests of allied socialist and social democratic parties in the European Parliament of the European Union (EU). Although a socialist group fostered cooperation among socialist parties in the Common Assembly of both the European Coal and Steel Community (ECSC) and the European Economic Community (later renamed the European Community) from 1953, the PES officially was established in 1992 at The Hague. It consists of more than 30 political parties from EU member countries and Norway. Several socialist and social-democratic parties in EU applicant and other countries (e.g., Croatia, Iceland, Israel, Switzerland, and Turkey) maintain associate or observer status. The PES is headquartered in Brussels.

The PES traces its roots to the Socialist International, an association of national socialist parties from Europe, Asia, Africa, Oceania, and the Western Hemisphere. In the initial sitting of the Common Assembly of the ECSC in 1952, members voted along ideological rather than national lines, encouraging the formation of ideological groupings within the organization's institutions. As a result of the European Economic Community's expansion in both size and scope, socialist parties created the Confederation of Socialist Parties of the European Community in 1974, and in 1992, following ratification of the Maastricht Treaty, the group adopted its current name. Socialist heads of government meet before annual EU summits to develop a coordinated strategy. The PES attempts to create common social democratic policies on such issues as EU enlargement and the development of a common security and foreign policy.