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 birthplace, or a restricted version of jus soli in which citizenship by birthplace is automatic only for the children of certain immigrants.
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. However, a frequent exception to lex soli is imposed when a child is born to a parent in the diplomatic or consular service of another state on a mission to the state in question.
Unrestricted jus soli
Chad (the choice to take Chadian citizenship, or that of the parents is made at 18 years of age)
Tanzania: Per the Tanzania Citizenship Act of 1995, "any child born within the borders of the United Republic of Tanzania, on or after Union Day, 26 April 1964, is granted citizenship of Tanzania, except for children of foreign diplomats."
Canada: Subsection 3(2) of the Citizenship Act states that Canadian citizenship by birth in Canada - including Canadian airspace and territorial waters - is granted to a child born in Canada even if neither parent was a Canadian citizen or permanent resident except if either parent was a diplomat, in service to a diplomat, or employed by an international agency of equal status to a diplomat. However, if neither parent was a diplomat, the nationality or immigration status of the parents do not matter. Some Conservative Party members wish to end birthright citizenship in Canada to the children of tourists and unauthorized immigrants.
Mexico: Article 30 of the Constitution of Mexico states that persons born in Mexican territory are natural-born citizens of Mexico regardless of their parents' nationality. The definition of "territory" includes vessels/aircraft flagged to Mexico travelling in international waters or airspace.
United States: The Citizenship Clause of the 14th Amendment to the United States Constitution, ratified in 1868, provides: "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 concept of birthright citizenship applying to the child born of a foreign national in the country without proper credentials has never been formally litigated, but the U.S. Supreme Court's decision in United States v. Wong Kim Ark (1898) allowed the government to deny citizenship to U.S.-born children only in the cases of children born to foreign diplomats and children born to enemy forces engaged in hostile occupation of the country's territory, and thus this decision is most often interpreted as barring the government from denying citizenship to a U.S.-born person based on the alienage of his or her parents. (see United States nationality law).
From 24 January 2020, the Trump administration adopted a new policy to make it more difficult for foreign nationals to obtain a nonimmigrant visa to travel to the US to give birth on US soil to ensure their children become US citizens, a practice commonly known as "birth tourism." Conservatives in the United States have often called for legislative reforms, including an amendment to the Citizenship Clause of the 14th Amendment, to end jus soli in the United States - particularly for children born to persons unlawfully present in the country.
Persons born in American Samoa (a U.S. territory) are not U.S. citizens at birth (they are non-citizen U.S. nationals, unless one of their parents is a U.S. citizen). In 2019, a federal court ruled that American Samoans are U.S. citizens, but the ruling was put on hold, and the litigation is ongoing.
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. Modification of ius soli has been criticized as contributing to economic inequality, the perpetuation of unfree labour from a helot underclass and statelessness. Ius soli has been restricted in the following countries:
Egypt: According to Article 4 of the Nationality Law of the Arab Republic of Egypt, children born in Egypt gain citizenship at birth if their father or mother was also born in Egypt.
Morocco: A person who was born in Morocco to parents also born in Morocco and whose immigration is legal, can register as a Moroccan two years prior to becoming adult.
Namibia: A person born in Namibia to a Namibian citizen parent or a foreign parent who is ordinarily resident in Namibia, is a Namibian citizen at birth (see Namibian nationality law).
Sudan: A person born before 1994 gains Sudanese nationality at birth if his father was also born in Sudan. If his father was not born in Sudan, he can apply to the Minister to be granted Sudanese nationality.
Tunisia: Individuals born in Tunisia are citizens by birth if their father and grandfather were born in Tunisia. Additionally, the person must declare before becoming an adult (20 years) that he wants to be a citizen.
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 to individuals that were "in transit" - to include "non-residents" (including individuals with expired residency visas and undocumented workers).
Bahrain: Children born to a foreign father with valid residency permits who himself was born in Bahrain have right to citizenship.
Cambodia: In 1996, Cambodia changed the law to grant citizenship to children born to foreign parents only if they are living legally in the Kingdom of Cambodia (under Article 4(2)(a) of the 1996 Nationality Law).
India: A person that was born in India from 26 January 1950 until 1 July 1987 is a citizen by birth, regardless of the parents' nationality. It began to be restricted in 1987. As of 2020, a person born in India is a citizen if at least one parent is a citizen, and the other parent is a citizen or a legal migrant. These measures were brought in largely in reaction to illegal migration from Bangladesh.
Pakistan: Pakistan has jus soli in practise. However, it is restricted to non-refugees. As was decided by Peshawar high court. Thus in practise Pakistan only has restricted jus soli. 
Malaysia: A person born in Malaysia on or after 16 September 1963 with at least one parent being a Malaysian citizen or permanent resident is automatically a Malaysian citizen (see Malaysian nationality law).
Mongolia: A person born in Mongolia to foreign parents with valid residency permits can apply for Mongolian nationality when they turn the age of 16. A child in Mongolian territory with unidentified parents can receive Mongolian citizenship (see Mongolian nationality law).
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. Furthermore, persons of Chinese ethnicity (wholly or partly) with PRC nationality born in Hong Kong are PRC nationals with Hong Kong permanent residence, even if their parents are non-PRC citizens (e.g. overseas-born Chinese). Non-PRC citizens born to non-PRC citizen Hong Kong permanent resident parents in Hong Kong also receive permanent residence of Hong Kong 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)).
Taiwan: Any child born to parents with Taiwanese citizenship, even those living abroad, can acquire Taiwanese nationality at birth. Children born in Taiwan to stateless parents or have unknown parentage are considered Taiwanese nationals at birth (see Taiwanese nationality law).
Thailand: Thailand operated a system of pure Ius soli prior to 1972. 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 for their child to be granted Thai citizenship at birth. Furthermore, someone who has Thai citizenship by sole virtue of Ius soli may be stripped of Thai citizenship under various conditions (such as living abroad), which does not apply to people who have Thai citizenship by virtue of Ius sanguinis.
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.
Israel: Children born in Israel who have never acquired another citizenship are eligible to apply for Israeli citizenship between their 18th and 21st birthday if they have lived in Israel for over 5 years (see Israeli citizenship law).
France: Children born in France (including overseas territories) to at least one parent who is either (i) a French citizen or (ii) born in France, automatically acquire French citizenship at birth. Children born to foreign parents who do not fulfil either of these two conditions may acquire citizenship from age 13 subject to residence conditions (see French nationality law). A child born in France to foreign parents becomes a French citizen automatically upon turning 18, provided that they reside in France on their 18th birthday and have had their primary residence in France for a total (but not necessarily continuous) period of at least 5 years since the age of 11.
Germany: prior to 2000 Germany's nationality law was based entirely on ius sanguinis, but now children born in Germany 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 resided in Germany for at least eight years prior to the child's birth. However, ius soli citizens will lose their German citizenship upon turning 23 unless they: (i) reside in Germany for at least 8 years during their first 21 years of life; or (ii) attend school in Germany for at least 6 years; or (iii) graduate from high school/college in Germany; or (iv) complete professional/vocational training in Germany.
Greece: Apart from regulations in past and historic nationality laws of Greece granting nationality ius soli,Greek Nationality Code of 2004 states that "A person born in Greek territory acquires by birth the Greek nationality if not acquiring alien nationality or is of unknown nationality". Additionally, as from 2015's amendment of 2004 Cod (Law 4332 of 2015, G.G. A/76/9 July 2015), a child born in Greece by foreign parents, shall acquire the right of Greek nationality with a combination of preliminary school attendance and parents' legal residence in Greece (5 years, 10 if the child is born prior to 5 years of legal residence). One year after the implementation of the law (as from July 2016), 6,029 children had been granted Greek nationality, out of 27,720 submitted applications.
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 resident with a permanent right to reside in Ireland or in Northern Ireland; or a legal resident residing three of the last four years in the country (excluding students and asylum seekers) (see Irish nationality law). The amendment was prompted by the case of Man Chen, a Chinese woman living in mainland United Kingdom who travelled to Belfast (Northern Ireland, part of the UK) to give birth in order to benefit from the previous rule whereby anyone born on any part of the island of Ireland was automatically granted Irish citizenship. The Chinese parents used their daughter's Irish (and thereby European Union) citizenship to obtain permanent residence in the UK as parents of a dependent EU citizen. Ireland was the last country in Europe to abolish unrestricted ius soli. (see Irish nationality law).
Luxembourg: A person born in Luxembourg is automatically a Luxembourg citizen if at least one of their parents was also born in Luxembourg. Additionally, a person born in Luxembourg to foreign, non-Luxembourg-born parents can become a Luxembourg citizen from the age of 12 if they have resided uninterrupted in Luxembourg for at least 5 years immediately prior to submitting the application, and if at least one of their parents lived in Luxembourg uninterrupted for at least 12 months immediately preceding their birth. Furthermore, a person born in Luxembourg to foreign, non-Luxembourg-born parents gains Luxembourg citizenship automatically upon reaching the age of 18, provided that they have lived uninterrupted in Luxembourg for the preceding 5 years and at least one of their parents lived uninterrupted in Luxembourg for at least 12 months immediately preceding their birth.
Portugal: A child born in Portuguese territory to who does not possess another nationality is a Portuguese citizen. Also, a person born to foreign parents who were not serving their respective States at the time of birth is a Portuguese citizen if the person declares that they want to be Portuguese and provided that one of the parents has legally resided in Portugal for at least two years at the time of birth.
Spain: A child born in Spain to foreign parents may acquire Spanish citizenship ius soli if either one of the parents was also born in Spain or neither of the parents can transmit their nationality to the child (such as stateless parents).
United Kingdom: Since 1 January 1983, at least one parent must be a British citizen or be legally "settled" in the country or upon the 10th birthday of the child regardless of their parent's citizenship status (see British nationality law).
Malta: A person born in Malta on or after 1 August 2001 is automatically a Maltese citizen if at least one of their parents is Maltese or was born in Malta. Anyone born in Malta before 1 August 2001, regardless of their parents' circumstances, is automatically a Maltese citizen, as the country conferred unconditional ius soli until this date (see Maltese nationality law).
Australia: Since 20 August 1986, persons born in Australia acquires Australian citizenship by birth only if at least one parent was an Australian citizen or permanent resident; or else after living the first ten years of their life in Australia, regardless of their parent's citizenship status (see Australian 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 (includes Australian citizens and Permanent Residents) (see New Zealand nationality law), or if to prevent being stateless.
Some countries that formerly observed jus soli have moved to abolish it entirely, conferring citizenship on children born in the country only if at least one of the parents is a citizen of that country.
Malta: Changed the principle of citizenship to jus sanguinis on 1 August 1989 in a move that also relaxed restrictions against multiple citizenship. However, anyone born in Malta before 1 August 2001 falls under unconditional jus soli and is a Maltese citizen.
^Parties to the Convention on the Reduction of Statelessness are also obligated to grant nationality to people who are born aboard ships flagged in the country or an aircraft registered in the country who would otherwise become stateless.
^Solodoch, Omer, and Udi Sommer (2020). "Explaining the birthright citizenship lottery: Longitudinal and cross-national evidence for key determinants". Regulation & Governance. 14: 63-81. doi:10.1111/rego.12197.CS1 maint: multiple names: authors list (link)
^ abcLung-chu Chen, An Introduction to Contemporary International Law: A Policy-Oriented Perspective (Oxford University Press, 2015), p. 223.
^Ivan Shearer & Brian Opeskin, "Nationality and Statelessness" Foundations of International Migration Law (eds. Brian Opeskin, Richard Perruchoud & Jillyanne Redpath-Cross: Cambridge University Press, 2012), p. 99.
^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)
^Ivan Shearer & Brian Opeskin, "Nationality and Statelessness" Foundations of International Migration Law (eds. Brian Opeskin, Richard Perruchoud & Jillyanne Redpath-Cross: Cambridge University Press, 2012), p. 99: "a well-established exception in customary international law is that a child born to parents who are foreign diplomats does not automatically acquire the nationality of a host State that applies jus soli."
^CODE DE LA NATIONALITE - ORDONNANCE No. 33/PG.-INT. - DU 14 AOUT 1962 - PORTANT CODE DE LA NATIONALITE TCHADIENNE "de la nationalité d'origine - CHAPITRE II - Art. 12 - Sont Tchadiens: Les enfants nés au Tchad de parents étrangers; toutefois, ils peuvent, si les deux ascendants ont la même nationalité, opter pour cette nationalité; ce droit d'option ne peut s'exercer que si la législation du pays dont les ascendants sont nationaux le permet." (Translation: "Chadian citizens include: Children born in Chad of foreign parents; however if both parents have the same nationality, they (the children) can opt for the parents' nationality, if the legislation of their parents' country permits it.")
^CODE DE LA NATIONALITE - ORDONNANCE No. 33/PG.-INT. - DU 14 AOUT 1962 - PORTANT CODE DE LA NATIONALITE TCHADIENNE "de la nationalité d'origine - CHAPITRE II - Art. 13 - L'option prévue aux articles 11 et 12 s'exerce à l'âge de dix-huit ans révolus. Toutefois, lorsque cette option est motivée par une reconnaissance postérieure à la majorité, l'intéressé doit l'exercer dans le délai d'un an qui suit la reconnaissance." (Translation: "The options presented in articles 11 and 12 deploy themselves at 18 years of age. However, if an individual recognizes their ability to follow these options after majority has been reached, a delay of 1 year must take place from the recognition before the options can be pursued.")
^The Constitution of Lesotho, chap. IV, sec. 38 | CHAPTER IV
CITIZENSHIP: 38. Persons born in Lesotho after the coming into operation of the Constitution
^Constitution of Barbados: CHAPTER II CITIZENSHIP Persons born in Barbados after 29 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.
^The Constitution of the Commonwealth of Dominica Chapter VII Citizenship 98"Every person born in Dominica after the commencement of this Constitution shall become a citizen of Dominica at the date of his birth: Provided that a person shall not become a citizen of Dominica by virtue of this section if at the time of his birth- a) neither of his parents is a citizen of Dominica and his father possesses such immunity from suit and legal process as is accorded to the enjoyment of a foreign sovereign power accredited to Dominica; or b) his father is a citizen of a country with which Dominica is at war and the birth occurs in a place then under occupation by that country."
^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.
^Constitution of Belize: PART III Citizenship, section 24"24. Every person born in Belize on or after Independence Day shall become a citizen of Belize at the date of his birth: Provided that a person shall not become a citizen of Belize by virtue of this section if at the time of his birth- his father or mother is a citizen of a country with which Belize is at war and the birth occurs in a place then under occupation by that country"
^Article 12a of the Federal Constitution (translated) says that Brazilians include, "a) those born in the Federative Republic of Brazil, even if of foreign parents, provided they are not in the service of your country". "Neoconstitucionalismo - Análise histórica". JusBrasil. a) os nascidos na República Federativa do Brasil, ainda que de pais estrangeiros, desde que estes não estejam a serviço de seu paí
^Faryal Nazir, Section 3.1.1 in Report on Citizenship Law: Pakistan, Robert Schuman Centre for Advanced Studies, European University Institute (December 2016): "Jus soli or citizenship by birth is recognized in the Act (Section 3 and 4). At the time of commencement of the Act, a person born in Pakistan could claim nationality if he was residing in Pakistan. Every person born in Pakistan after the commencement of this Act is deemed to be citizen of Pakistan by birth. The law denies citizenship to a person born in the country, if his father enjoys diplomatic immunity in Pakistan or if his father was an enemy or alien in Pakistan. Therefore, the children born to aliens in Pakistan are not accorded the privilege of citizenship."
^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.
^e.g., child born in Greece to alien parents after coming of age (Nationality law of 1835, Article 2), child born in Greece of unknown father and mother (Greek Civil Law of 1856, Article 14, Paragraph c), child born in Greece and not automatically acquiring another nationality (Greek Nationality Code of 1955, Article 1, Paragraph d)
^"Article 1 A child of foreigner parents born in Greece acquires the right to Greek nationality under the following preconditions: a) He/she has enrolled in the first grade of elementary school and is still attending Greek school at the time the application-declaration of paragraph 2 is being lodged. b) One of their parents has been living legally and continuously for at least five (5) years in the country before the child was born. In case the child was born before this five year period had been completed, then the necessary period of legal and continuous residence of the parents is extended to ten (10) years." See, Law 4332 of 2015
^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.