.gov.gov is the Internet top-level domain used by the United States federal government. It was one of the original top-level domains, established in January 1985.
The U.S. is the only country that has a government-specific top-level domain in addition to its ccTLD. Other countries typically use a second-level domain for this purpose, e.g., .gov.uk for the United Kingdom, .go.jp for Japan and .govt.nz for New Zealand.
Many U.S. federal agencies now use .fed.us rather than .gov. The Department of Defense and its subsidiary organizations use .mil.