Brazilian militias (Portuguese: Milícias), mainly in Rio de Janeiro, and some other cities of Brazil, are illegal mafia-like paramilitary groups made up of current and former police (Civil or Military) officers as well as Military Firefighters Corps officers, criminals, politicians, and military officers, operating also as a regular mafia by trade extortion and political influence.

Militias carry out both vigilante and organized crime activities. In the favelas, drug gangs like ADA and Red Command control trafficking and violence networks, openly selling drugs and carrying weapons as well as acting as the de facto authorities, building infrastructure and enforcing their own brand of law and order. These police-backed militias historically force out the drug traffickers in order to set up their own protection rackets, extorting residents and taxing basic services.

The militias have their roots in the death squads of the Brazilian military dictatorship in 1964. They emerged in the late 2000s, being made up of off-duty police officers with assistance from local businessmen who need protection from armed gangs.

Thanks to close ties to the official police force, the militias often enjoy the support of local politicians.

In 2006, the drug trafficking network Comando Vermelho started a conflict against the militias.

Brazilian militias have increasingly deep connections within the states' power dynamics.

Cesar Maia, Rio de Janeiro's mayor from 1993–1997 and 2001–2009, supported the rise of militias; in his words, militias were "community self-defense" and "an evil better than drug gangs".

In 2008, a group of journalists in disguise documenting a militia's activities were kidnapped and tortured by a militiamen. The journalists were held for seven hours before being freed without any harm. Although the identities of the journalists remain secret (with the exception of photojournalist Nilton Claudinho), two politicians were accused of orchestrating the kidnapping: Coronel Jairo [pt] and his son Dr. Jairinho.