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.
Article 29.3: The supremacy of the purposes and principles of the United Nations
Article 30: Nothing in this Declaration may be interpreted as implying for any State, group or person any right to engage in any activity or to perform any act aimed at the destruction of any of the rights and freedoms set forth herein.