WHOIS (pronounced as the phrase who is) is a query/response protocol (Protocol (computing)) that is widely used for querying databases in order to determine the registrant or assignee of Internet resources, such as a domain name, an IP address block, or an autonomous system (Autonomous system (Internet)) number Citation neededdate=February 2010. WHOIS lookups were traditionally performed with a command line interface application, but now many alternative web-based tools exist. WHOIS services are typically communicated using the Transmission Control Protocol (TCP). Servers listen to requests on the well-known port number 43.

The WHOIS system originated as a method for system administrators to obtain contact information for IP address assignments or domain name administrators. The use of the data in the WHOIS system has evolved into a variety of uses, including: * Supporting the security and stability of the Internet by providing contact points for network operators and administrators, including ISPs, and certified computer incident response teams; * Determining the registration status of domain names; * Assisting law enforcement authorities in investigations for enforcing national and international laws, including, for example, countering terrorism-related criminal offenses and in supporting international cooperation procedures. In some countries, specialized non-governmental entities may be involved in this work; * Assisting in the combating against abusive uses of Information communication technology, such as illegal and other acts motivated by racism, racial discrimination, xenophobia, and related intolerance, hatred, violence, all forms of child abuse, including pedophilia and child pornography, the trafficking in, and exploitation of, human beings. * Facilitating inquiries and subsequent steps to conduct trademark clearances and to help counter intellectual property infringement, misuse and theft in accordance with applicable national laws and international treaties; * Contributing to user confidence in the Internet as a reliable and efficient means of information and communication and as an important tool for promoting digital inclusion, e-commerce and other legitimate uses by helping users identify persons or entities responsible for content and services online; and * Assisting businesses, other organizations and users in combating fraud, complying with relevant laws and safeguarding the interests of the public.

PresentlyWhendate=July 2009 ICANN is undertaking a study to determine the uses and abuses of WHOIS information.Citation neededdate=July 2009 Other studies that are ongoing concern the accuracy of WHOIS information, and the effectiveness of the processes for reporting inaccurate public WHOIS information.Citation neededdate=July 2009

Due to the potential abuse of WHOIS information, the registrant of a domain is considered to be whoever controls the domains username/passwords, e-mail address, and administrative features.Citation neededdate=July 2009

WHOIS has a sister protocol called Referral Whois (RWhois).