Organized crime or criminal organizations is a transnational grouping of highly centralized enterprises run by criminals for the purpose of engaging in illegal activity, most commonly for the purpose of generating a monetary profit. The Organized Crime Control Act (U.S., 1970) defines organized crime as "The unlawful activities of [...] a highly organized, disciplined association [...]".

Mafia is a term used to describe a number of criminal organizations around the world. The first organization to bear the label was the Sicilian Mafia based in Italy, known to its members as Cosa Nostra. In the United States, "the Mafia" generally refers to the American Mafia. Other powerful organizations described as mafias include the Russian Mafia, the Chinese Triads, the Albanian Mafia, the Irish Mob, the Japanese Yakuza, the Neapolitan Camorra, the Calabrian 'Ndrangheta, the Indian Mafia, the Unione Corse, Serbian Mafia, and the Bulgarian mafia. There are also a number of localized mafia organizations around the world bearing no link to any specific racial background.

Some criminal organizations, such as terrorist organizations, are politically motivated (see VNSA). Gangs that become "disciplined" enough to be considered "organized". An organized gang or criminal set can also be referred to as a mob. The act of engaging in criminal activity as a structured group is referred to in the United States as racketeering.