The Irish mob (also known as the Irish-American mafia or Irish-American organized crime) is a collection of organized crime groups composed of largely ethnic Irish members which operate primarily in the United States, and have existed since the early 19th century. Originating in Irish-American street gangs – famously first depicted in Herbert Asbury's 1927 book, The Gangs of New York – the Irish Mob has appeared in most major U.S. and Canadian cities, especially in the Northeast and the urban industrial Midwest, including Boston, New York City, Philadelphia, Pittsburgh, Baltimore, Cleveland, and Chicago.

Irish-American street gangs, such as the Dead Rabbits (led by future Congressman John Morrissey) and Whyos, dominated New York's underworld for well over a century. Beginning in the 1880s and 1890s, however, they faced competition from gangs consisting of recently arrived Italians and Jews. The Five Points Gang (led by Paul Kelly) would rise to prominence during the early 1900s, strongly rivaled by the Hudson Dusters, the Gopher Gang, and others during the period.

In the early 1900s, with Italian criminal organizations such as the Morello crime family encroaching on the waterfront, various Irish gangs united to form the White Hand Gang. Although initially successful in keeping their Black Hand Italian rivals at bay, unstable leadership and infighting would lead to their eventual downfall. The murders of Dinny Meehan, Bill Lovett, and Richard Lonergan led to the gang's disappearance by 1925. The waterfront was then taken over by Italian mobsters Vincent Mangano, Albert Anastasia, and Joe Adonis. The Irish mob would re-emerge in USA's coal country and remain strong.

During the early years of Prohibition, "Big" Bill Dwyer emerged among many in New York's underworld as a leading bootlegger. However, following his arrest and trial for violation of the Volstead Act during 1925 and 1926, Dwyer's former partners were split among Owney "The Killer" Madden, the English-born former leader of the Gopher Gang, and Frank Costello against Jack "Legs" Diamond, "Little" Augie Pisano, Charles "Vannie" Higgins and renegade mobster Vincent "Mad Dog" Coll.

The Westies are an Irish American gang hailing from Hell's Kitchen on the West Side of Manhattan.

The most prominent members have included Eddie McGrath, James Coonan, Mickey Featherstone, James McElroy, and Edward Cummiskey.

In the Irish/Italian Mob War of the 1970s, the Irish mob saw an increased threat from the Italian Mafia as the Genovese crime family sought control over the soon-to-be-built Jacob K. Javits Convention Center. Also around this time, a power struggle emerged between Mickey Spillane and James Coonan, a younger upstart from Hell's Kitchen. Since the convention center was located in Spillane's Hell's Kitchen neighborhood, Spillane refused to allow any involvement by the Italians. Although the Italian gangsters greatly outnumbered the members of the Irish mob, Spillane was successful in keeping control of the convention center and Hell's Kitchen. The Italians, frustrated and embarrassed by their defeat by Spillane, responded by hiring a rogue Irish-American hitman named Joseph "Mad Dog" Sullivan to assassinate Tom Devaney, Eddie "the Butcher" Cummiskey, and Tom "the Greek" Kapatos, three of Spillane's top lieutenants.

In 1977 Spillane was murdered in a hail of bullets by assassins from the Genovese crime family. This prompted Coonan to form an alliance with Roy DeMeo of the Gambino crime family. The Genoveses decided that the Westies were too violent and well-led to go to war with and mediated a truce via the Gambinos.