au is the second-largest wireless carrier in Japan, with 60.398 million subscribers as of March 2021.

[1] According to the brand creator, the name 'au' is based on the Japanese verbs for 'meet' (会う) and 'unite' (合う) (both pronounced 'au').

IDO's network was based upon the NTT Hi-cap analog cellular system, and began operations in December 1988 in the Kanto and Tokai regions.

DDI's network was run by independent phone companies, and began service in 1989 using the TACS system elsewhere in Japan.

[4] au sponsors the Cerumo team in Japan Grand Touring Championship between 2001 to 2004.