Socialist Unity (Spanish: Unidad Socialista, US) was a Spanish party alliance formed to contest the 1977 general election by the People's Socialist Party (PSP) of Enrique Tierno Galván and the Federation of Socialist Parties (FPS). After the PSP and most of the parties within the FPS merged with the Spanish Socialist Workers' Party (PSOE) throughout 1978, the majority of US deputies and senators were absorbed into PSOE's parliamentary groups in the Congress and Senate.