ENUM, or E.164 Number Mapping, is a means of mapping international telephone numbers to special DNS records so that certain DNS information (such as IP addresses, e-mail addresses, etc.) can be associated with them.

International telephone numbers are systematically organized in the E.164 standard, while the Internet and IP-based networks use the Domain Name System (DNS) to map domain names to IP addresses and other resource information. ENUM effectively unites the telephone system with the IP world so that various DNS data records can be mapped to a single, portable personal identifier: a telephone number. It brings together the familiarity of the classic telephone network (the Public Switched Telephone Network, or PSTN) and the efficiency and cost-effectiveness of Internet telephony (Voice over IP, or VoIP), and allows the development of new IP-based multimedia services as well.