A domain name registrar is an organization that manages the reservation of Internet domain names. A domain name registrar must be accredited by a generic top-level domain (gTLD) registry or a country code top-level domain (ccTLD) registry. A registrar operates in accordance with the guidelines of the designated domain name registries.

Until 1999, Network Solutions Inc. (NSI) operated the registries for the com, net, and org top-level domains (TLDs). In addition to the function of domain name registry operator, it was also the sole registrar for these domains. However, several companies had developed independent registrar services. In 1996 one such company, NetNames, developed the concept of a standalone commercial domain name registration service which would sell domain registration and other associated services to the public, effectively establishing the retail arm of an industry with the registries being the wholesalers. NSI assimilated this model, which ultimately led to the separation of registry and registrar functions. In 1997, PGMedia filed an anti-trust suit against NSI citing the DNS root zone as an essential facility, and the US National Science Foundation (NSF) was joined as a defendant in this action. Ultimately, NSI was granted immunity from anti-trust litigation, but the litigation created enough pressure to restructure the domain name market. In October 1998, following pressure from the growing domain name registration business and other interested parties, NSI's agreement with the United States Department of Commerce was amended. This amendment required the creation of a shared registration system that supported multiple registrars. This system officially commenced service on November 30, 1999 under the supervision of the Internet Corporation for Assigned Names and Numbers (ICANN), although there had been several testbed registrars using the system since March 11, 1999. Since then, over 900 registrars have entered the market for domain name registration services.