KDDI Corporation (KDDI株式会社 KDDI Kabushiki Gaisha) (TYO: 9433) is a Japanese telecommunications operator formed on October 1, 2000 through the merger of DDI Corp. (Daini-Denden Inc.), KDD (Kokusai Denshin Denwa) Corp., and IDO Corp.[4] It has its headquarters in the Garden Air Tower in Iidabashi, Chiyoda, Tokyo.[5]

KDDI provides mobile cellular services using the "au by KDDI" brand. ISP network and solution services are provided under the au one net brand, while "au Hikari" is the name under which long-distance and international voice and data communications services and Fiber to the Home (FTTH) services are marketed. ADSL broadband services carry the brand name "ADSL One", and IP telephony over copper is branded as "Metal Plus".