The American Mafia, commonly referred to in North America as the Italian-American Mafia, the Mafia, or the Mob, is a highly organized Italian-American criminal society and organized crime group. The terms Italian Mafia and Italian Mob apply to these US-based organizations, as well as the separate yet related Sicilian Mafia or other organized crime groups in Italy, or ethnic Italian crime groups in other countries. These organizations are often referred to by its members as Cosa Nostra (Italian pronunciation: [ˈkɔːza ˈnɔstra, ˈkɔːsa -], "Our Thing" or "This Thing of Ours") and by the American government as La Cosa Nostra (LCN). The organization's name is derived from the original Mafia or Cosa Nostra, the Sicilian Mafia, with "American Mafia" originally referring simply to Mafia groups from Sicily operating in the United States.

The Mafia in the United States emerged in impoverished Italian immigrant neighborhoods in New York's East Harlem (or "Italian Harlem"), the Lower East Side, and Brooklyn; also emerging in other areas of the Northeastern United States and several other major metropolitan areas (such as Chicago and New Orleans) during the late 19th century and early 20th century, following waves of Italian immigration especially from Sicily and other regions of Southern Italy. Campanian, Calabrian and other Italian criminal groups in the United States, as well as independent Italian-American criminals, eventually merged with Sicilian Mafiosi to create the modern pan-Italian Mafia in North America. Today, the Italian-American Mafia cooperates in various criminal activities with Italian organized crime groups, such as the Sicilian Mafia, the Camorra of Campania and the 'Ndrangheta of Calabria. The most important unit of the American Mafia is that of a "family", as the various criminal organizations that make up the Mafia are known. Despite the name of "family" to describe the various units, they are not familial groupings.

The Mafia is most active in the Northeastern United States, with the heaviest activity in New York, Philadelphia, Baltimore, New Jersey, Pittsburgh, Buffalo, and New England, in areas such as Boston, Providence, and Hartford.