Every type of domain has a single organization that is responsible for maintaining the list of all the domain names of its own type (called a Top Level Domain – TLD). For example, the .COM TLD is run by a company called Verisign. The .CA domain (which is a country-code or ccTLD) is run by CIRA – the Canadian Internet Registration Authority.
Registries do not generally deal directly with the public, working instead through companies who deal directly with the end-user, ensuring that domain registrations are properly maintained and connecting securely to the registry to register, renew and edit domain information. Without going through a registrar, there is no way to register a new domain.
For more details on the history and structure of Domain Registrars, see the Wikipedia article here.
