This article discusses .us domain registration and Nexus requirements.
When you register a domain name that uses the .us top level domain (TLD), you must provide some additional information known as the Nexus requirements:
The first two fields are self-explanatory, but the Nexus Code (sometimes also called the Nexus Category) is not.
You must select the Nexus Code that best describes the person or entity registering the domain. The list of available Nexus Codes is:
C11 - United States citizen
C12 - Permanent resident of the United States of America, or any of its insular areas
C21 - A U.S.-based organization or company formed within one of the fifty (50) U.S. states, the District of Columbia, or any of the United States insular areas, or organized or otherwise constituted under the laws of a state of the United States of America, the District of Columbia or any of its insular areas, a U.S. federal, state, or local government entity or a political subdivision thereof.
C31 - A foreign entity or organization that has a bona fide presence in the United States of America or any of its insular areas who regularly engages in lawful activities (e.g., sales of goods or services or other business, commercial or non-commercial, including not-for-profit relations in the United States).
C32 - An entity that has an office or other facility in the United States.
Make sure you choose the appropriate code for your organization when you register a .us domain, or the application may be rejected.
For more information about the Nexus requirements for .us top-level domains, please visit the following sites: