customarylaw

Customary law refers to rules that have evolved from the long-standing practices of a community or of states, and from the belief that such practices are legally obligatory. It can be unwritten and operate alongside written laws, and in some systems it forms a core part of the legal order. In international law, customary law also arises from general and consistent practice accepted as law, and may be binding even without treaty texts.

In international law, the formation of customary norms requires two elements: state practice (repeated and widespread actions by states) and opinio juris (a belief that the practice is legally required). When a rule has become generally accepted in this way, it binds states regardless of formal consent. A persistent objector may resist becoming bound by a new customary rule. Some customary rules have attained jus cogens status, meaning they are non-derogable and universally binding, such as prohibitions against genocide, slavery, and torture.

Within domestic legal systems, customary law comprises customary norms that govern relations within a community, including personal status, family relations, property, and customary dispute resolution processes. Courts may recognize and apply customary norms, particularly where statutory law is silent or does not address local circumstances. customary law can coexist with statutes and constitutional rules, and it may be codified or displaced by legislation.

Critics note that customary law can be vague, slow to change, and difficult to prove. The evidence of practice and its legal significance can vary across communities and over time. In international and domestic contexts, customary law often interacts with human rights norms, reform efforts, and codification initiatives to shape modern legal systems.