The American Mafia (also known as American Cosa Nostra) is is an offshoot of the Sicilian Mafia that emerged on the East Coast of the United States during the late 19th century following waves of Sicilian and Southern Italian emigration (see also Italian diaspora). In North America, the Mafia often refers to Italian organized crime in general, rather than just traditional Sicilian organized crime.

The Italian American Mafia continues to dominate organized crime in the U.S. It uses this status to maintain control over much of both Chicago's and New York City's organized criminal activity, as well as criminal activity in other cities in the Northeast and across the country, such as Philadelphia, Las Vegas, New Orleans, and many others. The Mafia and its reputation have become entrenched in American popular culture, being portrayed in movies, TV shows, commercial advertising and video games.

The Italian American Mafia, specifically the Five Families of New York, has its roots in the Sicilian Mafia , but has been a separate organization in the United States for many years. Today, the American Mafia cooperates in various criminal activities with the different Italian organized crime groups, such as Camorra, which are headquartered in Italy. It is wrongly known as the "original Mafia", although it was neither the oldest criminal organization, nor the first to act in the U.S. In 1986, according to government reports, it was estimated that there are 1,700 members of "Cosa Nostra " and thousands of associate members. Reports also are said to include the Italian-American Mafia as the largest organized crime group in the United States and continues to hold dominance over the National Crime Syndicate, despite the increasing numbers of street gangs and other organizations of neither Italian nor Sicilian ethnicity.

American Cosa Nostra is most active in the New York metropolitan area, Philadelphia, New England (see the Patriarca crime family ), Detroit, and Chicago (see the Chicago Outfit ), but there are actually a total of 26 Cosa Nostra family cities around the United States.