a body of unwritten norms, called customs (rules of conduct), that have arisen spontaneously and have been sanctioned by the state. A legal system incorporates only those customs that function as legal norms—that is, those that reflect the interests and will of the economically and politically dominant class—and that the state adapts to specific political and economic conditions. Among historical law codes in which customs occupied an important place were the Code of Hammurabi, the Twelve Commandments, the Salic Law, and the Russkaia Pravda. In such Western European countries as France, customary law was important throughout the feudal period down to the formation of centralized absolute monarchies.

The development of bourgeois social relations and the expansion of production and commodity exchange required firm guarantees of the stability of these relations—a system of legal norms established by the state. In contemporary capitalist countries customary law is not of great importance, with the exception of court practice, where the norms of customary law are used to decide cases in accordance with established customs. Customary law plays a somewhat more important part in international relations, for example, in trade.

Soviet law recognizes customary law in instances where legal codes do not cover a particular social relationship. For example, custom may supplement the basic conditions of a contract, and it is used in resolving disputes over the division of property in a kolkhoz household. The Merchant Shipping Code of the USSR (arts. 134, 135, 149, and 151) states that agreements concerning such matters as the time allowed for loading operations and the payment due for delay after a ship has been loaded (demurrage) are concluded in conformity with the customs prevailing in the given port.