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, and is considered to be a groundbreaking skyscraper.

Upon completion in 1902, it was one of the tallest buildings in the city. The building sits on a triangular block formed by Fifth Avenue, Broadway and East 22nd Street, with 23rd Street grazing the triangle's northern peak. As with numerous other wedge-shaped buildings, the name "Flatiron" derives from its resemblance to a cast-iron clothes iron.

The neighborhood around it is called the Flatiron District after its signature building, which has become an icon of New York City. The building was designated a New York City landmark in 1966, was added to the National Register of Historic Places in 1979 and designated a National Historic Landmark in 1989.