Manhattan is one of the five boroughs of New York City, located primarily on Manhattan Island at the mouth of the Hudson River.

New York County, which has the same boundaries as the Borough of Manhattan (and which should not be confused with New York City), is the most densely populated county in the United States, with a 2007 population of 1,620,867US Census Bureau Annual Estimates of the Population for Counties: April 1, 2000 to July 1, 2007 living in a land area of 22.96 square miles (59.47  km²), or 70,595 residents per square mile (27,267/km²). It is also one of the wealthiest counties in the United States, with a 2005 personal income per capita above $100,000. Manhattan is the third-largest of New York's five boroughs in population but the smallest in area. It consists of Manhattan Island and several small adjacent islands: Roosevelt Island, Randall's Island, Ward's Island, Governors Island, Liberty Island, part of Ellis Island,1, New Jersey v. New York, 523 U.S. 767 (1998), accessed 2008-01-04. and U Thant Island; as well as Marble Hill, a small section on the mainland adjacent to the Bronx.

Manhattan is a major commercial, financial, and cultural center of both the United States and the world. Most major radio, television, and telecommunications companies in the United States are based here, as well as many news, magazine, book, and other media publishers. Manhattan has many famous landmarks, tourist attractions, museums, and universities. It is also home to the headquarters of the United Nations. Manhattan has the largest central business district in the United States, is the site of both the New York Stock Exchange and NASDAQ, and is the home to the largest number of corporate headquarters in the nation. It is the center of New York City and the New York metropolitan region, hosting the seat of city government and a large portion of the area's employment, business, and recreational activities.

The name Manhattan derives from the word Manna-hata, as written in the 1609 logbook of Robert Juet, an officer on Henry Hudson's yacht Halve Maen (Half Moon). A 1610 map depicts the name Manahata twice, on both the west and east sides of the Mauritius River (later named the Hudson River). The word "Manhattan" has been translated as "island of many hills" from the Lenape language.Holloway, Marguerite. "Urban tactics; I'll Take Mannahatta", The New York Times, May 16, 2004, accessed 2007-04-30. "He could envision what Henry Hudson saw in 1609 as he sailed along Mannahatta, which in the Lenape dialect most likely meant island of many hills.' The Encyclopedia of New York City offers other derivations, including from the Munsee dialect of Lenape: manahachtanienk ("place of general inebriation"), manahatouh ("place where timber is procured for bows and arrows"), or menatay ("island").