The Japanese dialects (方言, hōgen^?) comprise many regional variants. The lingua franca of Japan is called hyōjungo (標準語, lit. "standard language") or kyōtsūgo (共通語, lit. "common language"), and while it was based initially on the Tokyo dialect, the language of Japan's capital has since gone in its own direction to become one of Japan's many dialects. Dialects are commonly called -ben (弁, 辯, ex. Osaka-ben, lit. "Osaka speech"), sometimes also called -kotoba (言葉, ことば, ex. Shitamachi-kotoba, lit. "Shitamachi language") and -namari (訛り, なまり, ex. Tōhoku-namari, lit. "Tōhoku accent").

There is general agreement among linguists that the Ryukyuan languages of Okinawa Prefecture and the southern islands of Kagoshima Prefecture form a separate branch of the Japonic family, and are not Japanese dialects.

Regional variants of Japanese have been confirmed since the Old Japanese era. Man'yōshū, the oldest existing collection of Japanese poetry includes poems written in dialects of the capital (Nara) and eastern Japan (see also Old Japanese#Dialects), but other dialects were not recorded. The recorded features of eastern dialects were rarely inherited by modern dialects except for a few language islands such as Hachijo Island. In the Early Middle Japanese era, there were only vague records such as "rural dialects are crude". However, since the Late Middle Japanese era, features of regional dialects had been recorded in some books, for example Arte da Lingoa de Iapam, and the recorded features were fairly similar to modern dialects. The variety of Japanese dialects developed markedly during the Edo period because many feudal lords restricted the movement of people to and from other fiefs. Some isoglosses agree with old borders of han especially in Tohoku and Kyushu. From the Nara period to the Edo period, the dialect of Kinai (now central Kansai) had been the de facto standard Japanese, and the dialect of Edo (now Tokyo) took over in the late Edo period.