Unified Socialist Party of Catalonia

The Unified Socialist Party of Catalonia (Catalan: Partit Socialista Unificat de Catalunya, PSUC), was formed on 23 July 1936 through the unification of four left-wing groups; the Catalan Federation of Spanish Socialist Workers' Party (PSOE), the Partit Comunista de Catalunya (Communist Party of Catalonia, the Catalan branch of the Communist Party of Spain, PCE), the Unió Socialista de Catalunya (Socialist Union of Catalonia) and the Partit Català Proletari (Proletarian Catalan Party). Burnett Bolloten estimates that at unification, the party numbered some 2,500 members. Nine months later, the party ranks had swollen to 50,000 members.

The PSUC played a major role during the days of the Second Spanish Republic and the Spanish Civil War, and was the only regional party affiliated to Comintern. The PCE did not organize in Catalonia, but saw PSUC as its Catalan referent. This setup has been replicated by other Catalan communist groups. The setup is somewhat similar to the relation between the Christian Democratic Union of Germany and Christian Social Union of Bavaria.