10 East 40th Street or the Mercantile Building is a skyscraper on 40th Street in Midtown Manhattan, New York City. It is located in the middle of the block between Fifth and Madison avenues, extending south to 39th Street. Designed by Ludlow and Peabody and built by Jesse H. Jones, it was finished in 1929 and is an example of Renaissance Revival architecture. When it was built, it was the fourth-tallest tower in the world.

Ludlow and Peabody was an American architectural firm with offices in New York City formed by partners Charles S. Peabody and William Orr Ludlow in 1909. The firm continued in practice under that name until 1935.