The Flatiron Building, originally the Fuller Building^, is a triangular 22-story steel-framed landmarked building located at 175 Fifth Avenue in the borough of Manhattan, New York City, which is considered to be a groundbreaking skyscraper. Upon completion in 1902, it was one of the tallest buildings in the city at 20 floors high and one of only two skyscrapers north of 14th Street – the other being the Metropolitan Life Insurance Company Tower, one block east. The building sits on a triangular block formed by Fifth Avenue, Broadway, and East 22nd Street – where the building's 87-foot (27 m) back end is located – with East 23rd Street grazing the triangle's northern (uptown) peak. As with numerous other wedge-shaped buildings, the name "Flatiron" derives from its resemblance to a cast-iron clothes iron.

The building, which has been called "one of the world's most iconic skyscrapers and a quintessential symbol of New York City", anchors the south (downtown) end of Madison Square and the north (uptown) end of the Ladies' Mile Historic District. The neighborhood around it is called the Flatiron District after its signature building, which has become an icon of New York City.