Long Island is located in southeastern New York, United States. Stretching northeast into the Atlantic Ocean, Long Island contains four counties, two of which are boroughs of New York City (Queens and Brooklyn), and two of which (Nassau and Suffolk) are mainly suburban. In popular usage, however, the term “Long Island” generally refers only to Nassau and Suffolk counties in order to differentiate them from New York City.

The westernmost end of Long Island contains the New York City boroughs of Brooklyn (Kings County) and Queens (Queens County). The central and eastern portions contain the suburban Nassau and Suffolk counties. However, colloquial usage of the term "Long Island" refers only to Nassau and Suffolk counties. The more dense and urban Brooklyn and Queens are not usually referred to as "Long Island", since they are politically part of New York City, though before those counties amalgamated into the city, they were often so identified.

Nassau County is lined with pockets of rural affluence within the Gold Coast of the North Shore. South Shore communities are built along protected wetlands and white sandy beaches fronting on the Atlantic Ocean and Outer Barrier Islands.  Wealthy Americans and Europeans in the gilded age built lavish country homes on the North Shore of Nassau county. Today, (although many of the large estates have been demolished) many exist in their original state, while others have become parks, arboretums, universities and museums.

Owing to economic growth and the suburbanization of the metropolitan region after World War II, Nassau was the fastest growing county in the United States from the 1950s to the 1970s. Suffolk County remains less congested despite substantial growth in high technology and light manufacturing sectors since 1990. In its far east sections, Suffolk remains small-town rural, as in Greenport on the North Fork and some of the outward areas of The Hamptons, although summer tourism swells the population in those areas.

Long Island is geographically part of the Mid-Atlantic, however many towns and hamlets along the island's north shore and in eastern Suffolk County, such as Oyster Bay, Port Jefferson and Sag Harbor seem to resemble New England towns, while many of the towns and hamlets along the south shore, such as Long Beach, Valley Stream, and Babylon seem to resemble Mid-Atlantic coastal communities, especially those on the shore between New Jersey and Virginia.

Long Island is known for its affluence and high quality of life. According to Forbes Magazine, Nassau and Suffolk Counties are among the top 25 richest counties in America.  Additionally, Nassau County is the third richest county per capita in New York State, and the 30th richest in the nation. Suffolk County has redeveloped North Fork potato fields into a burgeoning wine region. The South Fork is known for beach towns, including the world-renowned Hamptons and for Montauk Point, home of Montauk Point Lighthouse at the eastern tip of the island.