Washington, D.C. (pronounced /ˈwɒʃɪŋtən ˌdiːˈsiː/, WOSH-ing-tən DEE-SEE), formally the District of Columbia and commonly referred to as Washington, the District, or simply D.C., is the capital of the United States, founded on July 16, 1790. Article One of the United States Constitution provides for a federal district, distinct from the states, to serve as the permanent national capital. The City of Washington was originally a separate municipality within the federal territory until an act of Congress in 1871 established a single, unified municipal government for the whole District. It is for this reason that the city, while legally named the District of Columbia, is known as Washington, D.C. The city shares its name with the U.S. state of Washington, which is located on the country's Pacific coast.

The city is located on the north bank of the Potomac River and is bordered by the states of Virginia to the southwest and Maryland to the other sides. The District has a resident population of 599,657; because of commuters from the surrounding suburbs, its population rises to over one million during the workweek. The Washington Metropolitan Area, of which the District is a part, has a population of 5.4 million, the eighth-largest metropolitan area in the country.

The centers of all three branches of the federal government of the United States are located in the District, as are many of the nation's monuments and museums. Washington, D.C. hosts 174 foreign embassies as well as the headquarters of the World Bank, the International Monetary Fund (IMF), the Organization of American States (OAS), the Inter-American Development Bank, and the Pan American Health Organization (PAHO). The headquarters of other institutions such as trade unions, lobbying groups, and professional associations are also located in the District.

Washington, D.C., is governed by a mayor and a 13-member city council. However, the United States Congress has supreme authority over the city and may overturn local laws. Residents of the District therefore have less self-governance than residents of the states. The District has a non-voting, at-large Congressional delegate, but no senators. D.C. residents could not vote in presidential elections until the ratification of the Twenty-third Amendment to the United States Constitution in 1961.