Jus sanguinis (Latin for "right of blood") is a right by which nationality or citizenship can be recognised to any individual born to a parent who is a national or citizen of that state. It contrasts with jus soli (Latin for "right of soil").

Usually a practical regulation of the acquisition of nationality or citizenship of a state by birth to a parent who is already a citizen of the state is provided by a derivative law called lex sanguinis. Most states provide a specific lex sanguinis, in application of the respective jus sanguinis, but citizenship is not normally automatically inherited. This is to avoid the creation of generations of overseas citizens with no real connection with the state, but still being able to claim rights such as immigration and protection from that state.

In many European countries, lex sanguinis still is the preferred means of passing on citizenship. This has been criticised on the grounds that, if the only means, it can lead to generations of people living their whole lives in the state without being citizens of it. More recently these countries have begun to move more towards use of lex soli, partially under the influence of the European Convention on Nationality. In most cases birth in the country plus the citizenship of at least one parent is sufficient.

Many states have a mixture of lex sanguinis and lex soli, including the United States, Canada, Israel, Germany, Greece, Britain, Ireland, and others.