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.

The PSUC became the major defender of the Catalan middle classes against land seizures advocated by the rival National Confederation of Labour and Workers' Party of Marxist Unification, organizing 18,000 tradesmen and artisans into the Catalan Federation of Small Businessmen and Manufacturers (GEPCI).

During the Francisco Franco regime (see Spain under Franco), the PSUC was outlawed and remained active clandestinely and in exile. The PSUC was the largest opposition party in Catalonia and upon the fall of the regime it became a mass party.

In 1977, during the Spanish transition to democracy, the PSUC was legalized. Gradually, the PCE and the PSUC started going in separate directions: PSUC became involved in Iniciativa per Catalunya (IC), and gradually ceased functioning as a separate party. When PSUC was completely submerged into IC in 1997, a splinter group refounded the party as PSUC viu (Living PSUC). PSUC viu became the new referent of PCE in Catalonia.