Lithuanian nationality law
Lithuanian nationality law operates on the jus sanguinus principle, whereby persons who have a claim to Lithuanian ancestry, either through parents, grandparents, great-grandparents may claim Lithuanian nationality. Citizenship may also be granted by naturalization. Naturalization requires a residency period, an examination in the Lithuanian language, examination results demonstrating familiarity with the Lithuanian Constitution, a demonstrated means of support, and an oath of loyalty. A right of return clause was included in the 1991 constitution for persons who left Lithuania after its occupation by the Soviet Union in 1940 and their descendants. Lithuanian citizens are also citizens  of the European Union and thus enjoy rights of free movement and have the right to vote in elections for the European Parliament. Post-Soviet implementation. In 1989, the legislature passed a nationality act granting automatic citizenship to those persons who could establish their own birth, or that of a parent or grandparent, within Lithuanian borders. Permanent residents not covered by these criteria were granted citizenship upon signing a loyalty oath. Language proficiency was not required. A 1991 treaty with Russia extended the definition of residency to those who had immigrated to Lithuania from Russia between 1989 and the ratification  of the treaty. Subsequent applicants for citizenship were required to meet a set of naturalization standards, including Lithuanian language testing. The citizenship requirements were the most liberal of those in the newly independent Baltic states. This is usually attributed to a relatively low level of immigration from other areas within the Soviet Union, resulting in a more ethnically homogenous population. Dual citizenship. In November 2006, the Constitutional Court of the Republic of Lithuania ruled that the Law on Citizenship (wording of 17 September 2002 with subsequent amendments and supplements) was "controversial, inconsistent and confusing". At issue was the possession of  dual citizenship; the provision extended the right of citizenship, and hence the right to vote, to members of the post-Soviet Lithuanian diaspora, which was concentrated in the United States, Canada, Australia, and Argentina, and their children, grandchildren, and great-grandchildren. The most notable member of this diaspora was Lithuanian President Valdas Adamkus, who had become a United States citizen; he formally renounced US citizenship before taking the oath of office. The petitioners held that basing citizenship on ethnic origin or nationality of the person violated the equality of persons and was discriminatory. The use and meaning of the term  repatriated was especially controversial. The Lithuanian Seimas (parliament) passed a temporary law, expiring in 2010, that granted dual citizenship in exceptional cases, most notably to those who were Lithuanian citizens prior to 1940 and who fled during the Soviet occupations, as well as to their children and grandchildren. The Constitution states that Lithuanian citizenship is acquired by birth except in certain cases established by law and that no person may be a citizen of Lithuania and another country or state at the same time, except in special cases. This provision of the Constitution can only be changed by a referendum . Currently, the law on citizenship allows dual citizenship only in exceptional cases for those whose ancestors left Lithuania before its independence from the Soviet Union 1990, but still had Lithuanian citizenship in 1940. There are some things to consider before someone could be able to pass the Lithuanian citizenship eligibility, and by having these, gives the person the right to claim Lithuanian citizenship. Persons who were citizens of independent Lithuania (between 1918 up to 1940) as well as their children, grandchildren, and great-grandchildren can restore Lithuanian citizenship. Persons of Lithuanian descent can restore dual Lithuanian citizenship if their ancestor  still had Lithuanian citizenship in 1940.  Dual citizenship can also be extended to descendants of Lithuanian citizens who were exiled to Siberia and stayed in Soviet Union countries.   During November 2010 the Seimas passed a law liberalizing dual citizenship requirements. President Dalia Grybauskaitė vetoed it, stating that: "According to the Constitution, dual citizenship is a rare exception, not a common case." On 23 June 2016, the Seimas passed a law further liberalizing dual citizenship requirements. It went into effect on 6 July 2016, amending the Law on Citizenship of the Republic of Lithuania (Law XI-1196 Dec 2, 2010). Article 7  of the Law on Citizenship as amended on 23 June 2016 lists the following criteria for dual citizenship: Some countries (such as Argentina, Uruguay and Mexico) do not allow renouncing their citizenship, so applicants might de facto keep dual citizenship even if they are eligible only for single Lithuanian citizenship. In certain cases, only restoration of Lithuanian citizenship as single Lithuanian citizenship is allowed. For example, persons that voluntarily left to former USSR countries prior to 1990 (i.e. were not deported) and have Lithuanian ancestors can restore Lithuanian citizenship but have to renounce their current citizenship. This does not apply  to the people that fled or emigrated from Soviet Union before 1990, these persons can restore dual citizenship, since it is considered that they fled occupation. In 2018, at the request of Lithuanian parliament, the constitutional court clarified that being a citizen of both Lithuania and another state at the same time is not acceptable. Those who left Lithuania after it regained independence in 1990 cannot hold dual citizenship therefore it could be changed only by referendum. The referendum to change the Constitution in order to allow Lithuanian citizens also to be citizens of other countries was held on  12 May 2019. Even though most of the voters were in favor of changing the Constitution - the referendum on Lithuanian dual citizenship failed because the turnout was too low. Citizenship of the European Union. Because Lithuania forms part of the European Union, Lithuanian citizens are also citizens of the European Union under European Union law and thus enjoy rights of free movement and have the right to vote in elections for the European Parliament. When in a non-EU country where there is no Lithuanian embassy, Lithuanian citizens have the right to get consular protection from the embassy of any  other EU country present in that country. Lithuanian citizens can live and work in any country within the EU as a result of the right of free movement and residence granted in Article 21 of the EU Treaty. Travel freedom of Lithuanian citizens. Visa requirements for Lithuanian citizens are administrative entry restrictions by the authorities of other states placed on citizens of Lithuania. In 2015, Lithuanian citizens had visa-free or visa-on-arrival access to 159 countries and territories, ranking the Lithuanian passport 10th in the world according to the Visa Restrictions Index. In 2017, the Lithuanian nationality is  ranked twenty-second in the Nationality Index (QNI). This index differs from the Visa Restrictions Index, which focuses on external factors including travel freedom. The QNI considers, in addition to travel freedom, on internal factors such as peace & stability, economic strength, and human development as well.