Jamaican posses, often referred to simply as posses or massives, is a general term referring to Jamaican organized crime gangs, based predominantly in Kingston, Spanish Town and Montego Bay, and in Jamaican diaspora communities in New York City, Miami, Toronto and London. First being involved in drugs and arms trafficking in the early 1980s, posses have links to the main Jamaican political parties, the Jamaica Labour Party (JLP) and the People's National Party (PNP).

Jamaican posses originated in the slums of Kingston as gangs of enforcers for the Jamaica Labour Party, led by Edward Seaga, and the rival People's National Party, headed by Michael Manley. The term "posse" was adopted from Hollywood Western films, which were popular in Kingston and other impoverished areas in Jamaica. Many posses are named after streets or neighborhoods in Jamaica. The widespread poverty and violence of Jamaican society provided the catalyst for the development of posses. Posses served as an informal system of control over local neighborhoods, and their development was connected to political nationalism and Rastafari. By the time of the 1980 Jamaican general election, the gangs had killed around 800 people. Although initially political in nature, posses evolved into structured and organized criminal gangs.

Following his election victory, Edwards Seaga launched a crackdown on political opponents, leading many rival posse members to flee to the United States to escape the political infighting of Jamaica. The two largest Jamaican posses in the U.S., the Shower Posse and the Spangler Posse, trace their origins to political parties in Kingston. Many of the other posses in the U.S. are splinter groups of the Shower and Spangler posses.

The first Jamaican posses in the U.S. were first identified in Brooklyn, New York in the 1970s. The groups' activities were initially confined largely to the New York City and Miami areas. Posses later expanded to other cities throughout the country, including Newark, Philadelphia, Hartford, Boston, Washington, D.C., Baltimore, Fort Lauderdale, Cleveland, Chicago, Kansas City, Dallas, Houston, Denver and Los Angeles. Applying their unique form of organization, structure, violence, and leadership, posses established a foothold in the illegal drug trade soon after their arrival in the U.S., initially in the importation and sale of marijuana before shifting emphasis to the street-level distribution of cocaine in the early 1980s. The change in emphasis from marijuana to cocaine was accompanied by an increased use of violence. Posses also established working relationships with Colombian cartels, traditional organized crime groups, and West Coast street gangs.

Jamaican gangs were largely responsible for the rapid spread of crack cocaine into the American heartland at the height of the crack epidemic in the mid-1980s. The posses' expansion into territories previously controlled by other drug gangs brought them into conflicts with African-American organized crime groups. According to the Bureau of Alcohol, Tobacco and Firearms (ATF), posses were responsible for approximately 1,000 murders between 1985 and 1989. By 1989, posses composed of 10,000 to 20,000 members and associates, most of them illegal aliens, affiliated with approximately 40 gangs operating in 15 metropolitan areas, and controlled an estimated 35 to 40 percent of the crack cocaine market in the U.S.

Members of the Shower Posse took up residence in Canada in the 1970s after fleeing Jamaica when the government of Michael Manley took power. The Shower Posse became heavily involved in the drug trade in Toronto through its connections with local gangs.

In the United Kingdom, Jamaican organized crime gangs are known as "yardies". Such gangs proliferated in the UK due to the country's association with former colonies in the Caribbean, and are typically involved in drug-related crime and gun crime. Jamaican crime groups have relatively small organizational structures and operate in association with other Jamaican gangs, although occasional conflicts between groups are manifested in street violence.

After taking control of the crack cocaine trade in London, yardie gangs spread throughout the south of England, and into parts of the Midlands, Wales, the north of England, and Scotland.