Nationality law is the branch of law concerned with the questions of nationality and citizenship, and how these statuses are acquired, transmitted, or lost. By custom, a state has the right to determine who its nationals and citizens are. Such determinations are usually made by custom, statutory law, or case law (precedent), or some combination. 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.
Broadly speaking, nationality law is based either on jus soli or jus sanguinis, or on a combination of the two. Jus soli (Latin: the law of the soil) is the principle by which a child born within a country's territorial jurisdiction acquires that country's nationality. Jus sanguinis (Latin: the law of the blood) is the principle by which a child acquires the nationality of his or her parents. Today, most if not all countries apply a mixture of these two principles: neither granting citizenship to everyone born within the country's jurisdiction, nor denying citizenship to the children born abroad.
International law generally recognizes the right of states to set their own policy concerning nationality. Nevertheless, there are a number of international treaties that are relevant to nationality law.