Comando Vermelho (Portuguese: [koˈmɐ̃du veʁˈmeʎu], Red Command or Red Commando), also known as CV, is a Brazilian criminal organization engaged primarily in drug trafficking, arms trafficking, protection racketeering, kidnapping-for-ransom, hijacking of armored trucks, loansharking, irregular warfare, narco-terrorism, and turf wars against rival criminal organizations, such as Primeiro Comando da Capital and Terceiro Comando Puro. The gang formed in the early 1970s out of a prison alliance between common criminals and leftist guerrillas who were imprisoned together at Cândido Mendes Penal Institute, a maximum-security prison on the island of Ilha Grande which was closed in 1994. The prisoners formed the alliance to protect themselves from prison violence and guard-inflicted brutality; as the group coalesced, the common criminals were infused with leftist social justice ideals by the guerrillas. In 1979, prison officials labeled the alliance "Comando Vermelho", a name which the prisoners eventually co-opted as their own. In the 1980s, the gang expanded beyond Ilha Grande into other prisons and the favelas of Rio de Janeiro, and became involved in the rapidly growing cocaine industry. Meanwhile, Brazil's shift towards democracy and the eventual end of the military dictatorship in 1985 allowed the leftist guerrillas to re-enter society; thus, the CV largely abandoned its left-wing ideology.

The cocaine trade brought the CV massive profits and growth; by the end of 1985 the gang controlled as much as 70% of the drug trade in Rio de Janeiro's favelas. During this period, the CV established trading relationships with Colombian cartels. However, the group's decentralized leadership structure and disputes over profits prompted infighting, causing splinter groups such as the Terceiro Comando and Amigos dos Amigos to emerge. Conflicts with these splinter groups, as well as fierce resistance to state crackdowns on their operations, drove a sharp uptick in violence in Rio and throughout Brazil throughout the late 1980s and into the 2000s.

Violence continued to escalate until 2008, when the state government implemented a new policy to mitigate violent crime, called Pacification, which used new permanent proximity-policing units (Unidade de Policia Pacificadora, or UPPs) to "maintain state control and provide social order" in favelas. Pacification proved initially successful; a sharp decline in violence between the state and the CV followed after implementation.

However, in 2013, Pacification efforts eroded, and widespread violent conflict between the CV and state forces quickly returned. Additionally, in 2016, a 20-year-old truce between the Primeiro Comando da Capital (PCC), a rival criminal organization based in São Paulo, and the CV broke down, sparking an outbreak in violent clashes between the two groups.

Today, while not as powerful as at its peak, the CV remains a significant presence in Rio and throughout Brazil; recent estimates suggest the group is the second-largest criminal organization in Brazil behind the PCC. InSight Crime reports the CV may boast as many as 30,000 members throughout Brazil. The gang continues to engage in drug trafficking, arms trafficking, and turf wars with rival gangs. Notably, in recent years a struggle has intensified between the CV, the PCC, and other rival gangs over control of trade routes and territory in the Amazon region.

The exact year that the Comando Vermelho was founded remains disputed, but sources agree the gang formed out of a prison alliance between leftist guerrillas and common criminals housed together during the 1970s by Brazil's military dictatorship at Cândido Mendes, a maximum security Brazilian prison.

Soon after their regime began in 1964, Brazil's military dictatorship faced a persistent challenge from leftist guerrilla rebels, made up largely of "middle-class intellectuals". In hopes of delegitimizing the rebels, in the early 1970s the Brazilian government began placing those they captured in prison alongside common criminals. One such prison, Candido Mendes, located on Ilha Grande, housed a mix of violent criminals and guerrillas in its notoriously brutal "Block B", or "The Pit". Inmates there were subject to frequent abuse at the hands of both their peers and the guards. The inmates banded together for mutual protection, shielding themselves from guard beatings and establishing a code of conduct for prisoners. Additionally, the guerrillas began to spread ideas about resistance, revolution, and social justice among the common criminals. As the alliance cemented, members introduced a common code of prison rules, designed to promote loyalty among members, reduce violence within the prison, and advance the common cause of the prisoners, while still maintaining a degree of autonomy for individual members to act as they desired.

In attempts to break up the alliance, prison officials moved inmate leaders to different wings and prisons, but this instead helped the group spread throughout the prison system. During this period prison officials gave the group its name: one official called the group "Comando Vermelho" in a memo to his colleagues. The name was adopted first by the press and then later by the group itself.