The Communist Party of Spain (Spanish: Partido Comunista de España; PCE) is a Marxist-Leninist party that, since 1986, has been part of the United Left coalition, which is part of Unidas Podemos.

The PCE was founded by 1921, after a split in the Spanish Socialist Workers' Party (Spanish: Partido Socialista Obrero Español; PSOE). The PCE was founded by those who opposed the social democratic wing of the PSOE, because the social democrat wing did not support the PSOE's integration in the Communist International founded by Vladimir Lenin two years prior. The PCE was a merger of the Spanish Communist Party (Spanish: Partido Comunista Español) and the Spanish Communist Workers' Party (Spanish: Partido Comunista Obrero Español). The PCE was first legalized after the proclamation of the Second Spanish Republic in April 1931. The republic was the first democratic regime in the history of Spain. The PCE gained much support in the months before the Spanish coup of July 1936, which marked the beginning of the Spanish Civil War, and it was a major force during the war as well. The Republicans lost, and Franco established a military dictatorship, under which the PCE was one of the most heavily repressed parties, with specific laws banning communist parties, among others.

Under the dictatorship, the PCE was the main opposition to the Francoist dictatorship. In the early years of the dictatorship, many PCE members joined the Spanish Maquis, a group of guerrillas who fought against the regime. Years later, the Maquis' power declined, and the PCE abandoned the military strategy. Instead, it chose to interfere in the only legal syndicate (which was part of the Francoist apparatus), the Vertical Syndicate.

Franco died on 20 November 1975, and two days later, Juan Carlos I was crowned. Juan Carlos I would lead the Spanish transition to democracy, a time when the PCE became also extremely relevant, due to Franco's anti-communist legacy. Prime Minister Adolfo Suárez legalized the PCE on 9 April 1977, a decision which was particularly controversial, but ended peacefully. The PCE largely contributed to the restoration of democracy in Spain during the lead of Secretary-General Santiago Carrillo.Since 1986, it is part of the United Left coalition. In its statutes, the PCE defines its goals as "democratically participate in a revolutionary transformation of society and its political structures, overcoming the capitalist system and constructing socialism in the Spanish State, as a contribution to the transition to socialism worldwide, with our goals set in the realization of the emancipating ideal of communism". It defines itself as revolutionary, internationalist, solidarity, republican, feminist, and secularist, specifically, of the laïcité variety.

The youth organization of PCE is the Communist Youth Union of Spain. PCE publishes Mundo Obrero (Workers World) monthly.