The Spanish Socialist Workers' Party (Spanish: Partido Socialista Obrero Español [paɾˈtiðo soθjaˈlista oˈβɾeɾo espaˈɲol] (listen); abbr. PSOE [peˈsoe] (listen)) is a social-democratic political party in Spain. The PSOE has been in government longer than any other political party in modern democratic Spain, namely from 1982 to 1996 under Felipe González; from 2004 to 2011 under José Luis Rodríguez Zapatero; and currently since 2018 under Pedro Sánchez.

The PSOE was founded in 1879, making it the oldest party currently active in Spain. The PSOE played a key role during the Second Spanish Republic, being part of coalition government from 1931 to 1933 and from 1936 to 1939, when the Republic was defeated by Francisco Franco in the Spanish Civil War. The party was then banned under Franco's dictatorship and its members and leaders were persecuted or exiled. The PSOE was only legalised again in 1977. Historically a Marxist party, it abandoned Marxism in 1979. Just like most mainstream Spanish political organizations since the mid-1980s, PSOE has been considered by experts to embrace a positive outlook towards European integration.

The PSOE has historically had strong ties with the General Union of Workers (UGT), a Spanish trade union. For a couple of decades, UGT membership was a requirement for PSOE membership. Since the 1980s, the UGT has frequently criticized the economic policies of the PSOE, even calling for several general strikes against the PSOE governments on 14 December 1988, 28 May 1992, 27 January 1994 and 29 September 2010, all jointly with the Workers' Commissions, another major trade union. Both the trade unions and the left have often criticized the economic policies of the PSOE for its economic liberal nature, have denounced the policies of deregulation and generalization of the precarious and temporary work, cuts in social benefits such as unemployment and retirement as well as the privatisations of big companies and public services.

The PSOE is a member of the Party of European Socialists, Progressive Alliance and the Socialist International. In the European Parliament, the PSOE's 20 Members of the European Parliament sit in the Socialists and Democrats European parliamentary group.