ENUM is a protocol that maps traditional telephone numbers onto internet domain names (ENUM domains). Like “normal” domains, the domain name system (DNS) is also used here, which assigns a domain name to a fixedly-mapped telephone number. This enables the use of a traditional telephone number as an address for internet services.

ENUM has been defined by the Internet Engineering Task Force (IETF )in the RFC 3761  document. In December 2004, Austria has started the commercial operation of ENUM as the first country worldwide. Therefore, the Austrian telecommunications regulator RTR  has assigned enum.at GmbH  with the administration of ENUM in Austria.