[4] The Spanish legal framework is considered to be one of the most restrictive in Europe in terms of citizenship acquisition.

[5] A preferential treatment in this regard is granted to former colonies, whose citizens also enjoy the privilege of not needing to renounce their original citizenship to acquire the Spanish one.

[7] The original text of the 1889 Civil Code was partially or wholly amended by the 23rd and 24th articles of the 1931 Constitution (which opened a way for exploring double citizenship agreements with Ibero–American countries), and the 1954, 1975, 1982, 1990, and 2002 laws.

[9][10] It is also the first constitution that emphasises that a español de origen ("Spaniard by origin") cannot be deprived of their nationality.

[10] On 13 July 1982, and in accordance to what had been established in the constitution, the first law regarding nationality was approved, which was in fact an amendment to the Spanish Civil Code in effect.

[15][11] Since the 1889 Civil Code came into effect, there have been various regulations requiring registration of births of Spaniards abroad, and limiting citizenship by descent to a specified number of generations.

[17] After that date, second generation born abroad Spaniards from the Iberosphere who were not already 18 or in legal majority (adulthood) by that date, and who held the other country's citizenship, are required to declare their intention to retain Spanish nationality to Spanish authorities within three years of majority (until age 21).

Spanish nationality can be acquired by naturalization, which is only granted at the discretion of the government through a royal decree, and under exceptional circumstances, for example to notable individuals.

[12][11][20] Under Article 22, to apply for nationality through residence it is necessary for the individual to have legally resided in Spain for:[12][14] In addition to meeting the residence requirement, applicants must pass the DELE and possess at least a level A2 certificate unless the applicant is a citizen of a country where Spanish is an official language, as well as pass a cultural and historical knowledge exam called the CCSE (Conocimientos Constitucionales y Socioculturales de España).

The Law establishes the right to Spanish nationality of Sephardi Jews with a connection to Spain.

[29] By July 2017 the government of Spain had registered about 4,300 applicants who had begun the process, and about 1,000 had signed before a notary public and filed their documents officially.

In 2007, the Congress of Deputies, under the government of prime minister José Luis Rodríguez Zapatero, approved the Law of Historical Memory with the aim of recognising the rights of those who suffered persecution or violence during the Spanish Civil War (1936-1939), and the dictatorial regime that followed (1939-1975).

[34][35][36] To the surprise of government officials, 92.5% of all applications were made by sons or daughters of Spaniards by origin regardless of their place of birth, and only 6.1% by grandchildren of refugees.

[34] Many applications under the law came from Cuba, which also offered those Cubans an ability to leave the island, and to also live and work in EU countries other than Spain.

This now included the grandchildren of people exiled under the Franco dictatorship, and the descendants of women who had lost their citizenship on marrying non-Spaniards.

The QNI considers, in addition, to travel freedom on internal factors such as peace & stability, economic strength, and human development as well.