Jus sanguinis (English: juss SANG-gwin-iss, yoos -⁠, Latin: [juːs ˈsaŋɡwɪnɪs]; 'right of blood') is a principle of nationality law by which citizenship is determined or acquired by the nationality or ethnicity of one or both parents. Children at birth may be citizens of a particular state if either or both of their parents have citizenship of that state. It may also apply to national identities of ethnic, cultural, or other origins. Citizenship can also apply to children whose parents belong to a diaspora and were not themselves citizens of the state conferring citizenship. This principle contrasts with jus soli ('right of soil'), which is solely based on the place of birth.

Today, almost all states apply some combination of jus soli and jus sanguinis in their nationality laws to varying degrees. Historically, the most common application of jus sanguinis is a right of a child to their father's nationality. Today, the vast majority of countries extend this right on an equal basis to the mother. Some apply this right irrespective of the place of birth, while others may limit it to those born in the state. Some countries provide that a child acquires the nationality of the mother if the father is unknown or stateless, and some irrespective of the place of birth. Some such children may acquire the nationality automatically while others may need to apply for a parent's nationality.