August 2006. Revised May 2010.
The following passage and its notes present some of the rules governing the spelling, punctuation, and capitalization of Washington, D.C., and related terms.
Washington, D.C., is the capital of the United States. Looking at the Capitol dome down East Capitol Street, Capitol Hillresidents may rue the District of Columbia’s lack of voting representation in Congress. Some federal agencies, such as the National Capital Planning Commission, may ignore the desires of the people of the District.
 The letters D.C. each get a period, since they are abbreviations for the term District of Columbia. Like a state name (“Gary, Indiana, is my home, sweet home”) it is set off by commas before and after.
 Capital, with an a, refers to a city that serves as the seat of a government. Ironically, it is not capitalized.
 Capitol, with an o, refers to a building that houses a legislature. Like the names of other specific buildings, e.g., the White House, the Capitol is capitalized.
 East, South, and North Capitol Streets are named after the building, so they are spelled with an o. The Capital Beltway is named after the city, so it is spelled with an a. There is no West Capitol Street. In its place, you will find the Mall, which, like other streets, is capitalized.
 Like East Capitol Street, Capitol Hill is named after the building, so it takes an o. Like other geographic names (Europe, the Sahara, etc.), neighborhood names are capitalized.
 The term District of Columbia emphasizes the legal entity, rather than the physical city. Since this phrase refers to matters of law and government, District of Columbia is more appropriate than Washington, D.C.
 Congress is capitalized when referring to the U.S. Congress.
 In documents produced by the federal government, federal is often capitalized. Follow that practice only when quoting directly.
 Agency names are capitalized. Formally, federal agencies’ names begin with United States, something to keep in mind when consulting bibliographies and library catalogs. National Capital is often used by the federal government to emphasize the region’s special function, compared to the more local Metropolitan Washington or Washington Metropolitan.
 The District refers specifically to the District of Columbia itself, as opposed to the larger metropolitan area.