Nationality is the legal relationship between a person and a state. Nationality affords the state jurisdiction over the person and affords the person the protection of the state. What these rights and duties are vary from state to state.

By custom and international conventions, it is the right of each state to determine who its nationals are. Such determinations are part of nationality law. In some cases, determinations of nationality are also governed by public international law—for example, by treaties on statelessness and the European Convention on Nationality.