KDDI Corporation is a Japanese telecommunication operator formed in October 2000 through the merger of DDI, KDD, and IDO Corp. KDDI provides mobile cellular services in the au brand, ISP network and solution services in the DION brand, and long-distance and international voice and data communications services.

On April 1st, 2002, KDDI launched 3G networks using cdma2000 1X technology. On November 28, 2003, au/KDDI launched cdma2000 1xEV-DO service in the CDMA 1X WIN brand.

au/KDDI has been very successful with its EZ wireless data services, EZweb, EZweb@mail, EZappli, EZchakuuta, ezmovie, and eznavigation (GPS), using the advanced WAP technology. It supports both J2ME and BREW application environments, which has caused confusion among users and developers.

au/KDDI is committed in providing compelling data services with packet discount packs. It is particular popular among students with special discount plans. All enabled by its efficient cdma2000 network.

As of end of 2003, au/KDDI has 15.977 million customers, among which 11.764 million (73.6%) are 3G cdma2000 subscribers. It is Japan's second-largest cellular operator with an increasing 20.0% market share.

TU-KA, an affiliated company of KDDI, is a 2G PDC cellular operator who did not apply a 3G license.