The contiguous United States are the 48 U.S. states on the continent of North America that are south of Canada and north of Mexico, plus the District of Columbia. The term excludes the states of Alaska and Hawaii, and all off-shore U.S. territories and possessions, such as Puerto Rico.

Together, the 48 contiguous states and D.C. occupy a combined area of 3,119,884.69 square miles (8,080,464.3 km²). Of this, 2,959,064.44 square miles (7,663,941.7 km²) is land, comprising 83.65% of U.S. land area. Officially, 160,820.25 square miles (416,522.5 km²) is water area, comprising 62.66% of the nation's water area. Its 2000 census population was 279,583,437, comprising 99.35% of the nation's population. Its population density was 94.484 inhabitants/sq mi (36.480/km²), compared to 79.555/sq mi (30.716/km²) for the nation as a whole. The 2010 census population was 306,675,006, comprising 99.33% of the nation's population, and a density of 103.639 inhabitants/sq mi (40.015/km²), compared to 87.264/sq mi (33.692/km²) for the nation as a whole.

The United States of America (commonly abbreviated to the United States, the U.S., the USA, America, and the States) is a federal constitutional republic comprising fifty states and a federal district. The country is situated mostly in central North America, where its forty-eight contiguous states and Washington, D.C., the capital district, lie between the Pacific and Atlantic Oceans, bordered by Canada to the north and Mexico to the south. The state of Alaska is in the northwest of the continent, with Canada to the east and Russia to the west, across the Bering Strait. The state of Hawaii is an archipelago in the mid-Pacific. The country also possesses several territories in the Pacific and Caribbean.

At 3.79 million square miles (9.83 million km²) and with over 312 million people, the United States is the third or fourth largest country by total area, and the third largest by both land area and population. It is one of the world's most ethnically diverse and multicultural nations, the product of large-scale immigration from many countries. The U.S. economy is the world's largest national economy, with an estimated 2011 GDP of $15.1 trillion (22% of nominal global GDP and over 19% of global GDP at purchasing-power parity). Per capita income is the world's sixth-highest.