Jus soli as an unconditional basis for citizenship is the predominant rule in the Americas, but among advanced economies (as defined by the International Monetary Fund), Canada and the United States are the only that observe unconditional birthright citizenship. Since the Twenty-seventh Amendment of the Constitution of Ireland was enacted in 2004, no European country grants citizenship based on unconditional jus soli. A study in 2010 found that only 30 of the world's 194 countries grant citizenship at birth to the children of illegal foreign residents, although definitive information was not available from 19 countries.
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 by birthplace, or a restricted version of jus soli in which citizenship by birthplace is not automatic for the children of certain aliens. Countries that have acceded to the 1961 Convention on the Reduction of Statelessness will grant nationality to otherwise stateless persons who were born on their territory, or on a ship or plane flagged by that country.
Jus soli is associated with permissive citizenship rights; most countries with unconditional jus soli laws tend to give birthright citizenship (and nationality) based on jus sanguinis rules as well, although these stipulations tend to be more restrictive than countries that use jus sanguinis as the primary basis for nationality.
At one time, jus sanguinis (right of blood) was the sole means of determining nationality in Europe (where it is still widespread in Central and Eastern Europe) and Asia. An individual belonged to a family, a tribe or a people, not to a territory. It was a basic tenet of Roman law.
An early form of partial jus soli dates from Cleisthenes' reforms of ancient Athenian law. It developed further in the Roman world, where citizenship was extended to all free inhabitants of the Roman Empire, especially with the Constitutio Antoniniana (Edict of Caracalla).
But it was much later, when the independence of the English colonies in America, and the French Revolution, laid the foundations for jus soli and with the social and economic development of the 19th and 20th centuries, and above all, the massive migrations to the Americas and Western Europe, that jus soli was established in a greater and greater number of countries.
The geographer Jared Diamond has calculated that if the application of jus soli since 1850 were abolished, 60% of Americans and 80% of Argentinians would lose their citizenship, and 25% of British and French.
At the turn of the 19th century, nation-states commonly divided themselves between those granting nationality on the grounds of jus soli (France, for example) and those granting it on the grounds of jus sanguinis (Germany, for example, before 1990). However, most European countries chose the German concept of an "objective nationality", based on race or language (as in Fichte's classical definition of a nation), opposing themselves to republican Ernest Renan's "subjective nationality", based on a daily plebiscite of one's belonging to one's Fatherland. This non-essentialist concept of nationality allowed the implementation of jus soli, against the essentialist jus sanguinis. However, today's increase of migrants has somewhat blurred the lines between these two antagonistic sources of right.
Lex soli is a law used in practice to regulate who and under what circumstances an individual can assert the right of jus soli. Most states provide a specific lex soli, in application of the respective jus soli, and it is the most common means of acquiring nationality. A frequent exception to lex soli is imposed when a child was born to a parent in the diplomatic or consular service of another state, on a mission to the state in question.
Unrestricted jus soli
- Antigua and Barbuda: Guaranteed by the Constitution. However, one government official told the Center for Immigration Studies that the country's current effort to tighten immigration policies may include an end to automatic birthright citizenship for children of illegal immigrants.
- Barbados: Guaranteed by the Constitution. However, the Barbados Ministry of Labour & Immigration recently proposed ending automatic birthright citizenship.
- Costa Rica (requires registration with the Costa Rican government before the age of twenty-five)
- El Salvador
- Saint Kitts and Nevis
- Saint Lucia
- Saint Vincent and the Grenadines
- Trinidad and Tobago 
- United States: The 14th Amendment to the United States Constitution provides that "all persons born or naturalized in the United States, and subject to the jurisdiction thereof, are citizens of the United States and of the State wherein they reside." The phrase "subject to the jurisdiction thereof" excludes children born to foreign diplomats and children born to enemy forces engaged in hostile occupation of the country's territory.Birthright citizenship is a separate concept from "natural-born citizen," a qualification for the office of President of the United States. See Birthright citizenship in the United States for more information.
Restricted jus soli
There is a trend in some countries toward restricting lex soli by requiring that at least one of the child's parents be a citizen, national, or legal permanent resident of the state in question at time of the child's birth, or requiring that at least one parent has resided in the country for a specific period of time. Modification of jus soli has been criticized as contributing to economic inequality, the perpetuation of unfree labour from a helot underclass, and statelessness. Jus soli has been restricted in the following countries:
- Australia: Since 20 August 1986, a person born in Australia acquires Australian citizenship by birth only if at least one parent was an Australian citizen or permanent resident or upon the 10th birthday of the child regardless of their parent's citizenship status (see Australian nationality law).
- Cambodia: In 1996, Cambodia changed the law to only grant citizenship to children born to foreign parents living legally in the Kingdom of Cambodia (under Article 4(2)(a) of the 1996 Nationality Law).
- Chile: The 1980 Constitution changed the Chilean nationality law to require that children born in Chile of non-citizen parents must request citizenship and be approved by the government.
- Colombia: a person born in Colombia with at least one parent being a Colombian citizen or resident is automatically a Colombian citizen (see Colombian nationality law).
- Dominican Republic: The constitution was amended on 26 January 2010. The amendment broadened the definition of the 2004 migration law - which excluded from citizenship children born individuals that were "in transit" - to include "non-residents" (including individuals with expired residency visas and undocumented workers).
- France: Children born in France (including overseas territories) to at least one foreign parent who is also born in France automatically acquire French citizenship at birth. Children born to foreign parents may request citizenship depending on their age and length of residence (see French nationality law).
- Germany: An exception to the increasing restrictiveness toward birthright citizenship, Germany, prior to 2000, had its nationality law based entirely on jus sanguinis. Now, children born on or after 1 January 2000 to non-German parents acquire German citizenship at birth if at least one parent has a permanent residence permit (and had this status for at least three years) and the parent was residing in Germany for at least eight years.
- Hong Kong: Since the July 1997 transfer of sovereignty over Hong Kong, most political rights and eligibility for most benefits are conferred to permanent residents regardless of citizenship; conversely, PRC citizens who are not permanent residents (such as residents of Mainland China and Macao) are not conferred these rights and privileges. The Basic Law provides that all citizens of the People's Republic of China (PRC) born in the territory are permanent residents of the territory and have the right of abode in Hong Kong. The 2001 case Director of Immigration v. Chong Fung Yuen clarified that the parents need not have right of abode, and as a consequence, many women from Mainland China began coming to Hong Kong to give birth; by 2008, the number of babies in the territory born to Mainland China mothers had grown to twenty-five times the number five years prior. Non-PRC citizens born to non-PRC citizen permanent resident parents in Hong Kong also receive permanent residence at birth. Other persons must have "ordinarily resided" in Hong Kong for seven continuous years in order to gain permanent residence (Articles 24(2) and 24(5)).
- Iran: Article 976(4) of the Civil Code of Iran grants citizenship at birth to persons born in Iran of foreign parents if one or both of the parents were themselves born in Iran. See Iranian nationality law.
- Ireland: On 1 January 2005, the law was amended to require that at least one of the parents be an Irish citizen; a British citizen; a child of a resident with a permanent right to reside in Ireland; or be a child of a legal resident residing three of the last four years in the country (excluding students and asylum seekers) (see Irish nationality law).
- Malaysia: a person born in Malaysia on or after September 16, 1963 with at least one parent being a Malaysian citizen or permanent resident is automatically a Malaysian citizen (see Malaysian nationality law).
- New Zealand: Since 1 January 2006 a person born in New Zealand acquires New Zealand citizenship by birth only if at least one parent was a New Zealand citizen or permanent resident (see New Zealand nationality law).
- South Africa: Since 6 October 1995 a person born in South Africa to South African citizens or permanent residents are automatically granted South African citizenship (see South African nationality law).
- Thailand: Thailand operated a system of pure jus soli prior to 1972, but afterwards, due to illegal immigration from Burma, the Nationality Act was amended to require that both parents be legally resident and domiciled in Thailand for at least five years in order for their child to be granted Thai citizenship at birth. Furthermore, someone who has Thai citizenship by sole virtue of jus soli may be stripped of Thai citizenship under various conditions (such as living abroad) which do not apply to people who have Thai citizenship by virtue of jus sanguinis.
- United Kingdom: Since 1 January 1983, at least one parent must be a British citizen or be legally "settled" in the country (see British nationality law)).
Abolition of jus soli
Some countries which formerly observed jus soli have moved to abolish it entirely, conferring citizenship on children born in the country only if one of the parents is a citizen of that country.
- India: Abolished jus soli on 3 December 2004, in reaction to illegal immigration from its neighbor Bangladesh. Jus soli had already been progressively weakened in India since 1987.
- Malta: Changed the principle of citizenship to jus sanguinis on 1 August 1989 in a move that also relaxed restrictions against multiple citizenship.
- jus soli, definition from merriam-webster.com.
- Vincent, Andrew (2002). Nationalism and particularity. Cambridge; New York: Cambridge University Press.
- Chicago Tribune: "Birthright citizenship benefits the country" by Ronald D. Rotunda September 16, 2010
- Texas Tribune: "Repeal Birthright Citizenship — and Then What?" by Morgan Smith August 16, 2010
- Feere, Jon (2010). "Birthright Citizenship in the United States: A Global Comparison". Center for Immigration Studies.
- "Nations Granting Birthright Citizenship". NumbersUSA. Retrieved 6 September 2009.
- Migration Policy Institute: "Citizenship in a Globalized World" By Greta Gilbertson January 2006
- 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.
- w:fr:Droit du sol
- Guimezanes, Nicole. "What Laws for Naturalisation?" The OECD Observer. Paris: June/July 1994. , Iss. 188; pg. 24, 3 pgs (Cites legislation for Australia, Austria, Belgium, Canada , Denmark, Finland, France, Ireland, Italy, Japan, Luxembourg, Netherlands, New Zealand, Norway, Portugal, Spain, Sweden, Switzerland, Turkey, United Kingdom and the United States)
- Constitution of Antigua and Barbuda: CHAPTER VIII CITIZENSHIP | PERSONS WHO AUTOMATICALLY BECOME CITIZENS AFTER COMMENCEMENT OF THIS CONSTITUTION | Section 113 The following persons shall become citizens at the date of their birth on or after 1st November 1981- a. every person born in Antigua and Barbuda: Provided that a person shall not become a citizen by virtue of this paragraph if at the time of his birth- i. neither of his parents is a citizen and either of them possess such immunity from suit and legal process as is accorded to the envoy of a foreign sovereign power accredited to Antigua and Barbuda; or ii. either of his parents is a citizen of a country with which Her Majesty is at war and the birth occurs in a place then under occupation by that country;
- Jon Feere, "Birthright Citizenship in the United States: A Global Comparison," Center for Immigration Studies, http://www.cis.org/birthright-citizenship
- Constitution of Barbados: CHAPTER II CITIZENSHIP Persons born in Barbados after 29th November 1966: Section 4: Every person born in Barbados after 29th November 1966 shall become a citizen of Barbados at the date of his birth: Provided that a person shall not become a citizen of Barbados by virtue of this section if at the time of his birth - a. his father possesses such immunity from suit and legal process as is accorded to an envoy of a foreign sovereign state accredited to Her Majesty in right of Her Government in Barbados and neither of his parents is a citizen of Barbados; or b. his father is an enemy alien and the birth occurs in a place then under occupation by the enemy.
- "It is the Department's view that the legislation should be amended to stipulate that (as in the United Kingdom and the Bahamas) children born in Barbados will not be deemed to be citizens of Barbados, unless at least one parent at the time of the birth, has permanent status in Barbados. In addition persons born in Barbados should not be deemed to be citizens where the parents are residing illegally in Barbados." http://www.foreign.gov.bb/Userfiles/File/IMMIGRATION%20POLICIES.pdf; see also, Jon Feere, "Birthright Citizenship in the United States: A Global Comparison," Center for Immigration Studies, http://www.cis.org/birthright-citizenship
- CITIZENSHIP LAW OF CANADA: PART I THE RIGHT TO CITIZENSHIP: Persons who are citizens Section 3. (1) Subject to this Act, a person is a citizen if (a) the person was born in Canada after February 14, 1977...
- The Constitution of Costa Rica: Title II ARTICLE 13: The following are Costa Ricans by birth: ...2. A child born abroad to a born Costa Rican father or mother, who is registered as such in the Civil Register by the will of the Costa Rican parent during its minority, or by his own will up to the age of twenty-five..."
- Fiji Constitution: chapter 3, Section 10 Citizenship by birth: Every child born in Fiji on or after the date of commencement of this Constitution becomes a citizen at the date of birth unless, at the date of birth: (a) a parent of the child has the diplomatic immunity accorded to envoys of foreign sovereign powers accredited to Fiji; and (b) neither parent is a citizen.
- Constitution of Jamaica Chapter II Citizenship 3B.-(1): Every person born in Jamaica shall become a citizen of Jamaica - a. on the sixth day of August, 1962, in the case of a person born before that date; b. on the date of his birth, in the case of a person born on or after the sixth day of August, 1962.
- The Constitution of Lesotho, chap. IV, sec. 38 | CHAPTER IV CITIZENSHIP: 38. Persons born in Lesotho after the coming into operation of the Constitution
- UN Refugee Agency: Pakistan Citizenship Act, 1951 Section 4. Citizenship by birth: Every person born in Pakistan after the commencement of this Act shall be a citizen of Pakistan by birth.
- Wikisource:Constitution of the Republic of Trinidad and Tobago/Chapter 2
- Constitution of Tuvalu Part III Section 45. Citizenship by birth: (1) Subject to subsections (3) and (4), a person born in Tuvalu on or after the date on which this Constitution took effect is a citizen of Tuvalu by birth." Note: section 3 pertains to children of foreign diplomats and section 4 pertains to children of belligerants at times of war
- Constitution of the United States Amendment XIV Section 1.
- United States v. Wong Kim Ark 169 U.S. 649 (1898); Ryan, John M. (27 August 2009). "Letters: U.S. citizenship". Silver City Sun-News. Retrieved 6 September 2009.
- Constitution of Venezuela (English translation) Chapter II, Nationality and Citizenship, Section One: Nationality, Article 32: Are Venezuelans* by birth: (1) Any person who was born within the territory of the Republic.
- Mancini, JoAnne; Finlay, Graham (September 2008). "'Citizenship Matters': Lessons from the Irish citizenship referendum". American Quarterly (American Quarterly) 60 (3): 575–599. doi:10.1353/aq.0.0034.
- NumbersUSA: "Nations Granting Birthright Citizenship" retrieved October 22, 2011
- title Law on Nationality of 20 August 1996 (unofficial translation)published by the United Nations High Commission for Refugees CHAPTER II KHMER NATIONALITY/CITIZENSHIP BY BIRTH ...shall obtain Khmer nationality/citizenship, by having been born in the Kingdom of Cambodia: a. any child who is born from a foreign mother and father (parents) who were born and living legally in the Kingdom of Cambodia.
- Constitution of the Republic of Chile, chap. II, art. 10, par. 1 (Spanish text; English version without recent changes) Article 10.- Chileans are: 1.- Persons born in the territory of Chile, with the exception of those children of foreigners who are in Chile serving their government, as well as those children of transient foreigners. However, all may opt for the Chilean nationality.
- Human Rights Brief: "The Constitution and the Right to Nationality in the Dominican Republic" October 29, 2010
- Soros.org: "A Crisis of Nationality: Dominicans of Haitian Descent" October 2013
- Huffington Post: "Dominican Republic To End Citizenship Of Those Whose Parents Entered Illegally" By EZEQUIEL ABIU LOPEZ and DANICA COTO September 27, 2013
- The Economist: "A storm in Hispaniola" December 7, 2013
- Junta Central Electoral: Inventario de extranjeros en Registro Civil 1929-2007 por mandato de Sentencia TC/0168/13 November 2013
- Respuesta al artículo del periódico New York Times: "Dominicans of Haitian Descent Cast Into Legal Limbo by Court"
- Chen, Albert H. Y. (2011). "The Rule of Law under 'One Country, Two Systems': The Case of Hong Kong 1997–2010". National Taiwan University Law Review 6 (1): 269–299. Retrieved 2011-10-04.
- "Babies Born in Hong Kong to Mainland Women". Hong Kong Monthly Digest of Statistics. September 2011. Retrieved 2011-10-04.
- "內地來港產子數目5年急增25倍 香港擬收緊綜援". People's Daily. 2008-03-10. Retrieved 2011-10-05.
- Basic Law of Hong Kong
- "Civil Code of Iran (last amended 1985)". United Nations High Commission for Refugees. Retrieved 2012-06-23.
- New Zealand Visa Bureau: "1000 kids face deportation or being orphaned for breaching New Zealand visa rules" October 7, 2011
- "Thailand". Republic of the Philippines: Office of the Solicitor General. Retrieved 2012-06-22.
- Yang, Bryant (2009). "Life and Death Away from the Golden Land: The Plight of Burmese Migrant Workers in Thailand". Thailand Law Journal 12 (1). Retrieved 2012-06-22.
- "Amendments to the Nationality Act 2008". Government Gazette of Thailand 125. 2008-02-27. Retrieved 2012-06-22.
- Sadiq, Kamal (2008). Paper Citizens: How Illegal Immigrants Acquire Citizenship in Developing Countries. Oxford University Press. p. 10. ISBN 978-0-19-537122-2.
- Bauböck, Rainer; Bernhard Perchinig; Wiebke Sievers (2007). Citizenship policies in the new Europe. Amsterdam University Press. p. 247. ISBN 978-90-5356-922-1.