In law, custom, or customary law consists of established patterns of behaviour that can be objectively verified within a particular social setting. The modern codification of civil law developed out of the customs, or coutumes of the middle ages, expressions of law that developed in particular communities and slowly collected and written down by local jurists. Such customs acquired the force of law when they became the undisputed rule by which certain entitlements (rights) or obligations were regulated between members of a community.
In international law, customary law refers to the Law of Nations or the legal norms that have developed through the customary exchanges between states over time, whether based on diplomacy or aggression. Essentially, legal obligations are believed to arise between states to carry out their affairs consistently with past accepted conduct. These customs can also change based on the acceptance or rejection by states of particular acts. Some principles of customary law have achieved the force of peremptory norms, which cannot be violated or altered except by a norm of comparable strength. These norms are said to gain their strength from universal acceptance, such as the prohibitions against genocide and slavery. Customary international law can be distinguished from treaty law, which consists of explicit agreements between nations to assume obligations. Many treaties, however, are attempts to codify pre-existing customary law.
The fact that a norm is customary has also a significance for the applicable rules of interpretation and may have the beneficial effect of limiting the power of States to make reservations or to denounce those treaties of IHL which have a high customarylaw content.
The decisions on customary humanitarian law of the Hague Tribunal for the Former Yugoslavia are the linear successors to the decisions of the Nuremberg Tribunals.
A declaration of the significance of customarylaw is incorporated into several IHL treaties, most notably in the so-called Martens clause, named for its drafter, Feodor de Martens, the adviser to the Russian Foreign Ministry at the beginning of the century.
Customary legal provisions that discriminated against women on the basis of gender and or status and deny them full participation in decision-making in rural and urban communities were identified as the first priority for concentration.
We work with an important distinction between the 'living' customarylaw (customary practices of the communities that lead their lives in accordance with customarylaw) and the customarylaw entrenched in law books and legislation enacted by governments that were in power before the democratic era.
While the traditional customarylaw of succession conflate rights with responsibilities, developments on the ground show that it is possible for customary inheritance systems to allow the widow to succeed to the marital property and to provide the heir with resources to discharge cultural responsibilities.