It was established in 2000 through the merger of DDI (第二電電, Daini Denden), KDD (ケイディディ), and IDO (日本移動通信, Nippon Idō Tsūshin).

In 2001, it merged with a subsidiary named Au, which was formed through the merger of seven automotive and mobile phone companies from the DDI-Cellular Group.

[citation needed] In December 2006, au by KDDI became the first carrier to provide an EV-DO Rev A service at a data rate of 3.1Mbit/s (downlink), 1.8 Mbit/s (uplink).

Toshiba, Casio, Sanyo, Kyocera, Hitachi, Sony Ericsson, Sharp, and Panasonic have manufactured the other models.

DDI Pocket, a PHS operator, was previously owned by KDDI but was spun off as Willcom which is now incorporated into Y!Mobile.

In August 2014, KDDI announced it was joining forces with five other global companies, including Google to build a 60 Tbit/s undersea data transmission cable linking the United States West Coast and Japan.

[13] In 2003, several class action complaints were filed against DDI for misrepresenting and/or failing to disclose material facts about the company's financial results.