15 William New York, formerly known as the William Beaver House, is a 47-floor residential skyscraper, which is located at 15 William Street on the corner of Beaver Street in the Financial District of Manhattan, New York City. It opened in 2008. It was designed by the New York firm of Tsao & McKown and built by André Balazs Properties. The building is 523 feet (159 m) high, and includes 320 units.
Noted for its brick exterior with yellow and dark grey panels between the windows, giving rise to the nickname "Post-It Note Building" the building was voted, in a non-scientific poll taken in September 2011, as "Manhattan's Ugliest Condo Tower". While originally intended to be entirely condominiums, 209 of the building's units were converted to rental in February 2011 due to sluggish sales.
In September 2007, one of the three penthouses was sold for 4.7 million dollars, the highest price per square foot ever in the Financial District. More recently, the building has seen its rental units nearly sell out, although occasional resident complaints, such as about credit card fees, still occur.
In 2015, 15 William was featured in a series of articles in Domino Magazine where designers redecorated several apartments throughout the building.