Casa Robino

Customary international law are those aspects of international law that derive from custom. Along with general principles of law and treaties, custom is considered by the International Court of Justice, jurists, the United Nations, and its member states to be among the primary sources of international law.
For example, laws of war were long a matter of customary law before they were codified in the Hague Conventions of 1899 and 1907, Geneva Conventions, and other treaties.
The vast majority of the world's governments accept in principle the existence of customary international law, although there are many differing opinions as to what rules are contained in it.