Madison Avenue is a north–south avenue in the borough of Manhattan in New York City, New York, that carries northbound one-way traffic. It runs from Madison Square (at 23rd Street) to meet the southbound Harlem River Drive at 142nd Street, passing through Midtown, the Upper East Side (including Carnegie Hill), East Harlem, and Harlem. It is named after and arises from Madison Square, which is itself named after James Madison, the fourth President of the United States.

Madison Avenue was not part of the original Manhattan street grid established in the Commissioners' Plan of 1811, and was carved between Park Avenue (formerly Fourth) and Fifth Avenue in 1836, due to the effort of lawyer and real estate developer Samuel B. Ruggles, who had previously purchased and developed New York's Gramercy Park in 1831, and convinced the authorities to create Lexington Avenue and Irving Place between Fourth Avenue (now Park Avenue South) and Third Avenue in order to service it.

The street's name has been metonymous with the American advertising industry since the 1920s. Thus, the term "Madison Avenue" refers specifically to the agencies and methodology of advertising. "Madison Avenue techniques" refers, according to William Safire, to the "gimmicky, slick use of the communications media to play on emotions."

Madison Avenue carries one-way traffic uptown (northbound) from East 23rd Street to East 135th Street, with the changeover from two-way traffic taking place on January 14, 1966, at which time Fifth Avenue was changed to one-way downtown (southbound). This changeover was accelerated by seven weeks due to the transit strike which began on January 1. Between East 135th Street and East 142nd Street, Madison Avenue carries southbound traffic only and runs parallel to the Harlem River Drive.

There are numerous structures designated as New York City Landmarks (NYCL), National Historic Landmarks (NHL), and National Register of Historic Places (NRHP) on Madison Avenue. From south to north (in increasing address order), they include:

The term "Madison Avenue" is often used metonymically to stand for the American advertising industry. Madison Avenue became identified with advertising after that sector's explosive growth in this area in the 1920s.

According to "The Emergence of Advertising in America", by the year 1861, there were 20 advertising agencies in New York City, and the New York City Association of Advertising Agencies was founded in 1911, predating the establishment of the American Association of Advertising Agencies by several years.

Among various depictions in popular culture, the portion of the advertising industry which centers on Madison Avenue serves as a backdrop for the AMC television drama Mad Men, which focuses on industry activities during the 1960s.