The rules of international law come from two main sources: treaties and customary international law, both of which are created by States. States are bound by the rules with which they have chosen to bind themselves—rules to which they have consented. ‘Where does international law come from?’ explains how international law works and considers the nature of customary international law and of treaties. Systems of customary law, including customary international law, are rooted in the regularity of an identified practice, whereas a treaty is an agreement between States that is legally binding. Often the broad principles set out in laws have to be mediated through detailed technical rules and standards.