(Arabic, custom), customary law among the Muslim peoples, as opposed to religious law, sharia. Many of the norms of adat—such as blood feuds and adoptive brotherhood—took shape when tribal relations were dominant. The decisions of courts of arbitration and the resolutions of meetings of rural communes played an important role in the formation and development of adat. The differences in local conditions account for the extreme diversity of adat. The norms of adat, which embody democratic principles to a certain extent, lost their initial character with the development of feudal relations; like feudal law, they were widely employed for the exploitation of workers.

In the USSR those norms of adat and sharia which contradict the norms of Soviet law are illegal. Certain actions sanctioned by adat are considered criminal by Soviet law, such as blood feuds, the acceptance of ransom to free one from blood feuds, bride money, and so on. The norms of adat which do not contradict Soviet law, such as wedding ritual, are considered custom.