Long Island is an island in southeastern New York, USA, jutting out into the Atlantic Ocean. It comprises four counties, two of which are boroughs of New York City, and two of which are suburbs of that city.

True to its name, the island is much longer than it is wide, jutting out some 118 miles (190 km) from New York Harbor, and varies in width between 12 and 23 miles (19 and 37 km) between the southern Atlantic coast and Long Island Sound. Long Island has an area of 1,401 square miles (3,629 km 2 ), making it the largest island in the continental United States and the 149th largest island in the world. It is connected to the mainland by several bridges and tunnels through New York City, and ferries to Connecticut from the middle of the island.

Long Island had a population of 7,448,618 as of the 2000 census, with the population estimated at 7,559,372 as of July 1, 2006, making it the most populated island in any U.S. state or territory. It is also the 17th most populous island in the world, ahead of Ireland, Jamaica and the Japanese island of Hokkaidō. Its population density is 5,470 people per square mile (2,110 per km 2 ).