New York–Northern New Jersey–Long Island, often referred to as the Tri-State Region, is the most populous metropolitan area in the United States and is also one of the most populous in the world.

The metropolitan area is defined by the United States Census Bureau as the New York-Northern New Jersey-Long Island, NY-NJ-PA Metropolitan Statistical Area (MSA), with an estimated population (as of 2005) of 18,747,320. The MSA is further subdivided into four metropolitan divisions. The 23-county metropolitan area includes ten counties in New York State, including the five boroughs of New York City, the two other counties of Long Island, and three in the lower Hudson Valley, twelve counties in Northern and Central New Jersey, and one county in northeastern Pennsylvania. The largest urbanized area in the United States is at the heart of the metropolitan area, the New York--Newark, NY--NJ--CT Urbanized Area (with a population of 17,799,861 as of the 2000 census).

Based on commuting patterns, the Census Bureau also defines a wider region consisting of the New York metropolitan area and five adjacent metropolitan areas, the New York-Newark-Bridgeport, NY-NJ-CT-PA Combined Statistical Area (CSA), with an estimated population of 21,903,623 (as of 2005). About one out of every fourteen Americans resides in this region, which includes seven additional counties in New York, New Jersey, and Connecticut, and is often referred to as the Tri-state Area and less commonly the Tri-State Region, leaving out Pennsylvania. However, the New York City television designated market area (DMA) includes Pike County, Pennsylvania.

This wider region includes the largest city in the United States (New York), the five largest cities in New Jersey (Newark, Jersey City, Elizabeth, Paterson, and Trenton) and the two largest cities in Connecticut (Bridgeport and New Haven). The total land area of the extended metropolitan area is .