WHOIS is a query and response protocol that is used to query databases that contain information about domain registrations and registrants. One can also learn about the IP address block that is used by the domain and other information that is all presented in an easy to read format based on the established WHOIS protocol. On the World Wide Wed, WHOIS lookups are quite common and frequent with many web pages helping to facilitate the task and formatting the resulting data. Most domain name registrars offer WHOIS lookups.

When one does a WHOIS query on a domain, the contact information of the resources assignee is normally returned. However, some registrars offer private registration, in which case the contact information of the registrar is shown instead along with a note about the registrants information being private. The reason for this privacy option being made available by registrars is that the organization ICANN requires that WHOIS return name, address, email address and phone number in response to a query which leaves many naturally wanting more privacy.