The 1977 Atocha massacre was an attack by right-wing extremists in the center of Madrid on January 24, 1977, which saw the assassination of five labor activists from the Communist Party of Spain (PCE) and the workers' federation Comisiones Obreras (CC.OO). The act occurred within the wider context of far-right reaction to Spain's transition to constitutional democracy following the death of dictator Francisco Franco. Intended to provoke a violent left-wing response that would provide legitimacy for a subsequent right-wing counter coup d'état, the massacre had an immediate opposite effect; generating mass popular revulsion of the far-right and accelerating the legalization of the long-banned Communist Party.

On the evening of January 24, three men entered a legal support office for workers run by the PCE on Atocha Street in central Madrid, and opened fire on all present. Those killed were labor lawyers Enrique Valdelvira Ibáñez, Luis Javier Benavides Orgaz and Francisco Javier Sauquillo; law student Serafín Holgado de Antonio; and administrative assistant Ángel Rodríguez Leal. Severely wounded in the attack were Miguel Sarabia Gil, Alejandro Ruiz-Huerta Carbonell, Luis Ramos Pardo and Dolores González Ruiz.

The perpetrators all had links to neo-fascist organizations in Spain opposed to democracy. Those involved in the massacre and their accomplices were sentenced to a total of 464 years in prison, although these terms were later significantly reduced and a number of the perpetrators escaped custody. Doubts remain as to whether all culpable persons were brought to justice.

The events surrounding the massacre are generally considered a crucial turning point in the consolidation of Spain's return to democracy in the late 1970s. Writing on the 40th anniversary of the massacre, journalist Juancho Dumall noted: "It was a terrorist act that marked the future of the country in a way that the murderers would never have suspected and, instead, was the one desired by the victims." Memorialized annually, across Madrid there are 25 streets and squares dedicated to the victims of the Atocha massacre.