Jus soli (English: juss SOH-ly, yooss SOH-lee), commonly referred to as birthright citizenship, is the right of anyone born in the territory of a state to nationality or citizenship.

Jus soli was part of the English common law, in contrast to jus sanguinis, which derives from the Roman law that influenced the civil-law systems of mainland Europe.

Jus soli is the predominant rule in the Americas; explanations for this geographical phenomenon include: the establishment of lenient laws by past European colonial powers to entice immigrants from the Old World and displace native populations in the New World, along with the emergence of successful Latin American independence movements that widened the definition and granting of citizenship, as a prerequisite to the abolishment of slavery since the 19th century. Outside the Americas, however, jus soli is rare. Since the Twenty-seventh Amendment of the Constitution of Ireland was enacted in 2004, no European country grants citizenship based on unconditional or near-unconditional jus soli.

Almost all states in Europe, Asia, Africa and Oceania grant citizenship at birth based upon the principle of jus sanguinis ("right of blood"), in which citizenship is inherited through parents rather than birthplace, or a restricted version of jus soli in which citizenship by birthplace is automatic only for the children of certain immigrants.

Jus soli in many cases helps prevent statelessness. Countries that have acceded to the 1961 Convention on the Reduction of Statelessness are obligated to grant nationality to people born in their territory who would otherwise become stateless persons. The American Convention on Human Rights similarly provides that "Every person has the right to the nationality of the state in whose territory he was born if he does not have the right to any other nationality."