The Serbian mafia, or Serbian organized crime, are various criminal organizations based in Serbia or composed of ethnic Serbs in the former Yugoslavia and Serbian diaspora. The organizations are primarily involved in smuggling, arms trafficking, drug trafficking, human trafficking, assassinations, heists, assault, protection rackets, murder, money laundering and illegal gambling. Ethnic Serb organized crime groups are organized horizontally; higher-ranked members are not necessarily coordinated by any leader. The Serbian mafia is estimated to earn €125 billion annually, with its annual earnings on the cocaine market in Europe worth €5.4 billion. According to criminologists and law enforcement authorities, the Serbian mafia is the most powerful in Europe.

A gangster is a criminal who is a member of a gang. Most gangs are considered to be part of organized crime. Gangsters are also called mobsters, a term derived from mob and the suffix -ster. Gangs provide a level of organization and resources that support much larger and more complex criminal transactions than an individual criminal could achieve. Gangsters have been active for many years in countries around the world. Gangsters are the subject of many novels, films, television series, and video games.