This text offers a concise and accessible coverage of the historical background, the organization and policies of the 15 social democratic parties in the European Union with a focus on the 1945-1990s period. It combines an updated study of the evolution of each party's ideology, sociology and policies, with attention also to the impact of European integration on the fortunes of social democratic forces. The book can be used as a reference text by academics, students and political practitioners and contains contact details and reference information for each party. The book is aimed at departments of politics (European politics, politics of European Union, comparative politics and government, political ideology), sociology, history, European studies; trade unions, Left political parties in EU; political commentators, journalists, and party research centres.