Extell Development is a New York City-based real estate development company founded by former diamond dealer Gary Barnett in the early 1990s. The company was known as Intell Management and Investment until 2005.

Its projects have included the 1,000-foot One57; the W Hotel in Times Square, which opened in 2002; 45 Walker Street, an office-to-loft-condominium conversion in Tribeca; the International Gem Tower in the Diamond District, and One Manhattan Square at  225 Cherry Street.

Extell is also the developer of the 1,550-foot supertall at 217 West 57th Street along Billionaires' Row dubbed Central Park Tower, the tallest residential building in the world (as of 2021). The 179-unit tower has a projected sellout of $4 billion, making it the most expensive condominium project in New York City. Closings kicked off in early 2021.