The republican repression in Madrid (1936–1939) was a series of measures applied against presumed enemies of the Second Spanish Republic. Repressive actions were organised by state services, party militias and hybrid structures. Some activities were carried out as part of legal procedures and might have involved various judiciary, but others remained on the verge of legal framework or clearly beyond it. Legally-sanctioned repressive actions included execution, expropriations, fines, dismissal, jail, relocation, forced labour or loss of civil rights. Extrajudicial violence included execution, rape, mutilation, torture, humiliation, incarceration, destruction or takeover of property. The climax of repressions took place in 1936, but they continued during the following years. Their total scale remains unclear; fragmentary figures indicate that one institution detained at least 18,000 people in 1936. The number of the executed is disputed; two personal lists produced contain around 9,000 and around 11,500 names. Historians do not agree on most issues related to the Spanish Civil War repressions, including the ones of Madrid in 1936-1939.

Usera Tunnel was a scam operated by Republican security units during the Spanish Civil War. It took place in Madrid between mid-October and mid-November 1937. Its objectives were twofold; one was to capture supposed supporters of the Nationalists, who were hiding in Madrid, mostly in premises of foreign diplomatic missions; another was to enrich the scammers by robbing the victims of money and valuables. The scammers floated rumors about an underground tunnel, allegedly located in the Madrid suburb of Usera and running below the frontline to the Nationalist-held sector. Posing as corrupted Republican militiamen they lured at least 67 individuals, who were imprisoned, robbed and killed in army premises near the frontline. Three individuals charged with operating the scam were later apprehended and executed in the Francoist Spain; one more died in prison. Casimiro Duran Muñoz, the officer deemed to have been the chief engineer of the project, was last seen in 1938 and his later fate is unknown.