are Japanese kanji readings borrowed from Chinese during the Tang dynasty, from the 7th to the 9th centuries; a period which corresponds to the Japanese Nara period. They were introduced by, among others, envoys from Japanese missions to Tang China. Kan-on should not be confused with , which were later phonetic loans.
Kan-on are based on the central Chang'an pronunciation of Middle Chinese. The syllable Kan is a reading of Middle Chinese: (xan<sup>H</sup>) as per Japanese phonology, referring to the Han dynasty, which had Chang'an as its capital city. Furthermore, Kan () has also become a description for all things Chinese, e.g., kanji ('Chinese characters').
Kan'on partly displaced the earlier go-on, which were "just imitations of Korean imitations, but Kan-on were imitations of the real thing."
A minority of characters never had their kan-on transmitted to Japan; their kan-on are sometimes reconstructed in Japanese dictionaries although not specifically marked as such. A few dictionaries go as far as to discard attested kan-on in favour of more systematic pronunciations.