The term honji suijaku or honchi suijaku (本地垂迹) in Japanese religious terminology refers to a theory widely accepted until the Meiji period according to which Indian Buddhist deities choose to appear in Japan as native kami to more easily convert and save the Japanese. The theory states that some kami are local manifestations of Buddhist deities. The two entities form an indivisible whole called gongen and in theory should have equal standing, but this was not always the case. In the early Nara period, for example, the honji was considered more important and only later did the two come to be regarded as equals. During the late Kamakura period it was proposed that the kami were the original deities and the buddhas their manifestations.

A gongen (権現), literally "incarnation", was believed to be the manifestation of a buddha in the form of an indigenous kami, an entity who had come to guide the people to salvation, during the era of shinbutsu-shūgō in premodern Japan. The words gonge (権化) and kegen (化現) are synonyms for gongen. Gongen shinkō (権現信仰) is the term for belief in the existence of gongen.