.us (United States) domain is the Internet country code top-level domain ( ccTLD ) for the United States , established in 1985. Registrants of .us domains must be United States citizens, residents, or organizations, or a foreign entity with a presence in the United States. Most .us domain registrants in the country have registered for .com, .net, .org and other gTLDs, rather than .us, which has traditionally primarily been used by many state and local governments (although any entity had the option of registering a .us domain name). In particular, the domains .gov and .mil have been reserved for U.S. usage.

The original administrator of .us domain was Jon Postel of the Information Sciences Institute at the University of Southern California. He administrated .us domains under a sub-contract USC/ISI had from SRI International (who held the .us domains and the Generic top-level domains contract with the United States Department of Defense ) and later Network Solutions (who held the .us and the Generic top-level domains contract with the National Science Foundation ). Registrants could only register .us third-level domains or higher in a geographic and organizational hierarchy. The vast majority of the geographic sub-domains in .us were delegated to various private entities and .us domain registrants would register with the delegated administrator for the level they wished to register in, not directly with the .us domain administrator. However, from April 2002, second-level domains became available for registration. The .us domain is currently administered by NeuStar Inc. under a United States Department of Commerce contract.

Since the official release of .us as a second-level domain, it has been adopted and developed by a number of private corporations and local citizenry. The .us country code is no longer in the exclusive realm of only governmental agencies.