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Jus sanguinis (Latin: right of blood) is a principle of nationality law by which citizenship is not determined by place of birth but by having instead one or both parents who are citizens of the state or more generally by having state citizenship or membership to a nation determined or conferred by -ethnic, cultural or other- descent or origin, e.g. by belonging to a Diaspora, i.e. without necessarily having progenitors that are or were citizens of that state per se. It contrasts with jus soli (Latin for "right of soil").
At the end of the 19th century, the French-German debate on nationality saw the French, such as Ernest Renan, oppose the German conception, exemplified by Johann Fichte, who believed in an "objective nationality", based on blood, race or language. Renan's republican conception explains France's early adoption of jus soli. Many nations have a mixture of jus sanguinis and jus soli, including the United States, Canada, Israel, Germany (as of recently), Greece, and Ireland.
Apart from France, jus sanguinis is still the most common means of passing on citizenship in many continental European countries. Some countries provide almost the same rights as a citizen to people born in the country, without actually giving them citizenship. An example is Indfødsret in Denmark, which provides that upon reaching 18, non-citizen residents can decide to take a test to gain citizenship.
Unlike France, some European states (in their modern forms) are postempire creations within the past century. States arising out of the Austro-Hungarian Empire and the Ottoman Empire had huge numbers of ethnic populations outside of their new boundaries, as do most of the former Soviet states. Several had long-standing diasporas that did not conform to 20th century European nationalism and state creation.
In many cases, jus sanguinis rights were mandated by international treaty, with citizenship definitions imposed by the international community. In other cases, minorities were subject to legal and extra-legal persecution and their only option was immigration to their ancestral home country. States offering jus sanguinis rights to ethnic citizens and their descendants include Italy, Greece, Turkey, Bulgaria, and Romania. Each is required by international treaty to extend those rights.
Lex sanguinis 
Many countries provide immigration privileges to individuals with ethnic ties to these countries (so-called leges sanguinis):
- Armenia: Article 14 of the Constitution of the Republic of Armenia (1995) provides that "[i]ndividuals of Armenian origin shall acquire citizenship of the Republic of Armenia through a simplified procedure." This provision is consistent with the Declaration on Independence of Armenia, issued by the Supreme Soviet of the Republic of Armenia in 1989, which declared at article 4 that "Armenians living abroad are entitled to the citizenship of the Republic of Armenia".
- Bulgaria: Article 25 of the 1991 constitution specifies that a "person of Bulgarian origin shall acquire Bulgarian citizenship through a facilitated procedure." Article 15 of the Law on Bulgarian Citizenship provides that an individual "of Bulgarian origin" (ethnicity) may be naturalized without any waiting period and without having to show a source of income, knowledge of the Bulgarian language, or renunciation of his former citizenship. This approach has been a tradition since the foundation of Bulgaria in 1879, when large numbers of ethnic Bulgarians remained outside of the state. Bulgaria and Greece were subject to a population exchange following the Second Balkan War. The conditions of the treaty settlement mandated that they accept individuals claiming respective ethnic origin.
- Croatia: Article 11 of the Law on Croatian Citizenship allows emigrants and their descendants to acquire Croatian nationality upon return, without passing a language examination or renouncing former citizenship. In addition, Article 16 allows ethnic Croatians living outside Croatia "acquire Croatian citizenship" by making a written declaration and by submitting proof of attachment to Croatian culture.
- Estonia: Article 36 of Estonian constitution states the right of every Estonian to come and live in Estonia.
- Finland: Finnish law provides a right of return to ethnic Finns from the former Soviet Union, including Ingrians. Applicants must now pass an examination in one of the official languages of the country, Finnish or Swedish. Certain persons of Finnish descent who live outside the former Soviet Union also have the right to establish permanent residency, which would eventually entitle them to qualify for citizenship.
- Germany: Article 116(1) of the German Basic Law (constitution) confers, within the range of the laws regulating the peculiarities, a right to citizenship upon any person who is admitted to Germany (in its borders of 1937) as "refugee or expellee of German ethnic origin or as the spouse or descendant of such a person." At one time, ethnic Germans living abroad in a country in the former Eastern Bloc (Aussiedler) could obtain citizenship through a virtually automatic procedure. Since 1990 the law has been steadily tightened to limit the number of immigrants each year. It now requires immigrants to prove language skills and cultural affiliation. Article 116(2) entitles persons (and their descendants), who were denaturalised by the Nazi government, to be renaturalised if they wish. Those among them, who took their residence in Germany after May 8, 1945 are automatically to be considered as Germans. Both reguations, (1) and (2), provided for a considerable group of Poles and Israelis, residing in Poland and Israel, who are simultaneously Germans.
- Greece: Ethnic Greeks can obtain Greek citizenship by two methods under the Code of Greek Nationality. Article 5 allows ethnic Greeks who are stateless (which, in practice, includes those who voluntarily renounce their nationality) to obtain citizenship upon application to a Greek consular official. In addition, ethnic Greeks who join the armed forces acquire automatic citizenship by operation of Article 10, with the military oath taking the place of the citizenship oath. This position arises from the fact that approximately 85% of known ethnic Greeks were outside the boundaries when the country was formed, and 40% remained outside the final boundaries at the beginning of World War I. Most were de jure stripped of their host country citizenship with the outbreak of war if the host country was at war with Greece. In the late 19th century, Greece had a wider diaspora because of poverty and limited opportunities.
- Hungary: Section 4(3) of the Act on Nationality permits ethnic Hungarians (defined as persons "at least one of whose relatives in ascendant line was a Hungarian citizen") to obtain citizenship on preferential terms after one year of residence. In addition, the "Status Law" of 2001 grants certain privileges to ethnic Hungarians living in territories that were once part of the Austro-Hungarian Empire. It permits them to obtain an identification card but does not confer the right to full Hungarian citizenship. According to the latest Citizenship Law adopted in 2010, anybody, possessing certain evidences (certificates, documents) of his or her Hungarian roots from around the World can apply for Hungarian Citizenship. The interview is lead in Hungarian either in Hungary or at one of the Consulates abroad.
- India: A child born in India must have at least one parent who is an Indian citizen to be conferred citizenship. Persons with at least one Indian grandparent may apply for a Person of Indian Origin card, provided that neither the applicant nor any ancestor has ever been a citizen of Pakistan, Bangladesh, Nepal, Sri Lanka, Afghanistan, or China. The government may add other countries to the list. This card is a travel document and permits the holder to enter and stay in India without a visa, work, start a business, own land, and attend educational institutions, but it does not give the right to vote or hold office. In addition, persons of Indian origin who are nationals of countries not on the list may apply for Overseas Indian Citizenship, which confers similar rights and also permits the holder to apply for full Indian nationality after one year of residence.
- Ireland: Under Irish nationality law, any person with an Irish grandparent can become an Irish citizen by being registered in the Foreign Births Register at an Irish embassy or consular office, or at the Department of Foreign Affairs in Dublin. Such an individual may also pass his entitlement to Irish nationality on to his children by registering in the Foreign Births Register, provided he or she registered as an Irish citizen with the Foreign Births Register before the birth of those children. The minister may also waive the usual requirements for naturalisation as an Irish citizen for those of "Irish descent or Irish associations" although this power is rarely used.
- Israel: In addition to Israeli citizenship being granted to all ethnic groups and religions (a) by virtue of birth in Israel or (b) by naturalisation after five years' residency and the acquisition of a basic knowledge of Hebrew, (c) the Law of Return confers an automatic right to citizenship on any immigrant to Israel who is Jewish by birth or conversion, or who has a Jewish parent, grandparent or spouse or who is the spouse of a child of a Jew or the spouse of a grandchild of a Jew.
- Italy: Possibly alone in this respect, Italian nationality law bestows citizenship jure sanguinis. There is no limit of generations for the citizenship via blood, but the Italian ancestor born in Italian territories before 1861 had to die after 1861 anywhere in the world without losing the Italian citizenship before death to being able to continue the jure sanguinis chain. This is required because 1861 is the year that the Unification of the Italian territory took place. Another constraint is that each descendant of the ancestor through whom citizenship is claimed jure sanguinis can pass on citizenship only if the descendant was a citizen at the time of the birth of the person to whom they are passing it. So, if any person in the chain renounces or otherwise loses the Italian citizenship and then has a child, that child is not an Italian citizen jure sanguinis. A further constraint is that until January 1, 1948, Italian law did not permit women to pass on citizenship. Persons born before that date are not Italian citizens jure sanguinis if their line of descent from an Italian citizen depends on a female at some point before 1948.
- Kiribati: Articles 19 and 23 of the constitution provides, "Every person of I-Kiribati descent... shall... become or have and continue to have thereafter the right to become a citizen of Kiribati.... Every person of I-Kiribati descent who does not become a citizen of Kiribati on Independence Day... shall, at any time thereafter, be entitled upon making application in such manner as may be prescribed to be registered as a citizen of Kiribati."
- Liberia: the Liberian constitution allows only people "of sub-saharan African descent" (regardless of cultural or national affiliation) to become citizens.
- Poland: The definition of Polish citizenship has been based for years on article 34 of the Polish Constitution; this article is based on a Jus sanguinis right to citizenship. Moreover any child born by Polish parent(s) is a de jure citizen of Poland unless its parent(s) request by the 90th day since its birth the Polish citizenship to be abolished. In 1967-1968 the Communist State illegally and in violation of the Polish Constitution, issued Jews emigrating from Poland to Israel a so called travel document (reading that the bearer of the travel document for exit from Poland without the right to return) instead of passports, in effect taking away their Polish citizenship for having supposedly, in emigrating or traveling to Israel, denounced it themselves. The first independent Polish President Lech Kaczyński, the constitutional guardian of the Polish constitution, ordered the reinstatement of Polish citizenship to all Poles that were forced against their will by the communist government to give up the rights to citizenship.Consequently the presidential order to reinstate their citizenship was proclaimed as having citizenship unlawfully revoked. Those citizens who were forced by the State to relinquish their citizenship against their will between 1920 and 1989, have had their citizenship reinstated by a presidential decree. The reinstatement of Citizenship has nothing to do with any naturalization criteria.
Ref. Polish Journal of Law (Dziennik Ustaw).
- Rwanda: The Rwandan constitution provides that "[a]ll persons originating from Rwanda and their descendants shall, upon their request, be entitled to Rwandan nationality."
- Serbia: Article 23 of the 2004 citizenship law provides that the descendants of emigrants from Serbia, or ethnic Serbs residing abroad, may take up citizenship upon written declaration.
- Slovakia: Persons with at least one Slovak grandparent and "Slovak cultural and language awareness" may apply for an expatriate identity card entitling them to live, work, study and own land in Slovakia. Expatriate status is not full citizenship and does not entitle the holder to vote, but a holder who moves his or her domicile to Slovakia may obtain citizenship under preferential terms. As a Slovak citizen living abroad with a child born abroad, I would like to add the following: Slovakia grants full Slovak citizenship to children of Slovak parents (one or both parents) irrespctible of the place of birth.
- South Korea: South Korean nationality law grants special status to some descendants of ethnic Koreans.
- Spain: Those born to an original Spaniard (whether or not the parent still retains Spanish citizenship or is still living) are entitled to original Spanish nationality. (Original Spaniards are those who were born with Spanish nationality, no matter where they were born). The grandchildren of those who emigrated due to political or economical reasons are also entitled to original Spanish nationality. Citizenship on preferential terms may be obtained after one year's residence for grandchildren of original Spanish citizens, as well as any person who can claim Sephardic Jewish ancestry. For citizens of Andorra, Portugal, Latin America, the Philippines, or Equatorial Guinea, the required residency period is two years, but it is ten years for all other foreigners.
- Turkey: Turkish law allows persons of Turkish origin and their spouse and children, to apply for naturalization without the five-year waiting period applicable to other immigrants. Turkey and Greece reciprocally expelled their minorities in the early 1920s after World War I. They were mandated by international treaty to accept incoming populations as citizens based on ethnic background.
- Ukraine: Article 8 of the Law on Citizenship of Ukraine permits any person with at least one Ukrainian grandparent to become a citizen upon renunciation of the former nationality.
See also 
- Dora Kostakopoulou (2008). The Future Governance of Citizenship. Cambridge University Press. pp. 26–27.
- Vink, M. and G.R. de Groot (2010). Birthright Citizenship: Trends and Regulations in Europe. Comparative Report RSCAS/EUDO-CIT-Comp. 2010/8. Florence: EUDO Citizenship Observatory, pp. 35.
- Armenia Constitution
- The Federal Expellee Law (German: Bundesvertriebenengesetz), § 6, specifies that also foreign citizens of states of the Eastern Bloc (and their desdendants), who were persecuted between 1945 and 1990 for their German ethnicity by their respective governments, are entitled to become Germans. The argument was that the Federal Republic of Germany had to administer to their needs because the respective governments in charge of guaranteeing their equal treatment as citizens severely neglected or contravened that obligation.
- English translation of the Polish Constitution.