Limpieza de sangre (Spanish: [limˈpjeθa ðe ˈsaŋɡɾe]), limpeza de sangue (Portuguese: [lĩˈpezɐ ðɨ ˈsɐ̃ɡɨ], Galician: [limˈpeθa ðe ˈsaŋɡe]) or neteja de sang (Catalan: [nəˈtɛʒə ðə ˈsaŋ]), literally "cleanliness of blood" and meaning "blood purity", played an important role in the modern history of the Iberian Peninsula.
It referred to those who were considered pure " Old Christians", without recent Muslim or Jewish ancestors, or within the context of the empire ( New Spain and Portuguese India) usually to those without ancestry from the American Indians, Aboriginal Asian, or Aboriginal African people.
By the end of the Reconquista and the conversion or expulsion of Muslim mudéjars and Sephardi Jews, the populations of Portugal and Spain were all nominally Christian. Out of Spain's population of 7 million, this included up to a million recent converts from Islam and 200,000 converts from Judaism, who were collectively referred to as " New Christians". Converts from Judaism were referred to as conversos or more pejoratively marranos, and converts from Islam were known as Moriscos. A commonly leveled accusation was that the New Christians were false converts, secretly practicing their former religion as Crypto-Jews or Crypto-Muslims. Nevertheless, the concept of purity of blood came to be more focused on ancestry than of personal religion. The first statute of purity of blood appeared in Toledo, Spain, 1449,  where an anti-converso riot succeeded in obtaining a ban on conversos and their descendants from most official positions. Initially, these statutes were condemned by the monarchy and the Church; however, in 1496, Pope Alexander VI approved a purity statute for the Hieronymites. 
This stratification meant that the Old Christian commoners could assert a right to honor even if they were not in the nobility. The religious and military orders, guilds and other organizations incorporated in their by-laws clauses demanding proof of cleanliness of blood. Upwardly mobile New Christian families had to either contend with their plight, or bribe and falsify documents attesting generations of good Christian ancestry. 
The claim to universal hidalguía (lowest nobility) of the Basques was justified by intellectuals like Manuel Larramendi (1690–1766)  because the Umayyad conquest of Hispania had not reached the Basque territories, so it was believed that Basques had maintained their original purity, while the rest of Spain was suspect of miscegenation. The universal hidalguía of Basques helped many of them to positions of power in the administration.  This idea was reinforced by the fact that, as a result of the Reconquista, a large number of Spanish noble lineages were already of Basque origin. 
Tests of limpieza de sangre had begun to lose their utility by the 19th century; rarely did persons have to endure the grueling inquisitions into distant parentage through birth records. However, laws requiring limpieza de sangre were still sometimes adopted even into the 19th century. For example, an edict of 8 March 1804 by King Ferdinand VII resolved that no knight of the military orders could wed without having a council vouch for the limpieza de sangre of his spouse. 
Official suppression of such entry requirements for the Army was enacted into law on 16 May 1865,  and extended to naval appointments on 31 August of the same year. On 5 November 1865, a decree allowed children born out of wedlock, for whom ancestry could not be verified, to be able to enter into religious higher education (canons).  On 26 October 1866, the test of blood purity was outlawed for the purposes of determining who could be admitted to college education. On 20 March 1870, a decree suppressed all use of blood purity standards in determining eligibility for any government position or any licensed profession. 
The discrimination was still present into the 20th century in some places like Majorca. No Xueta (descendants of the Majorcan conversos) priests were allowed to say Mass in a cathedral until the 1960s. 
The earliest known case judging Limpieza de Sangre comes from the Church of Cordoba, that explained the procedure to judge the purity of blood of a candidate as follows: Kneeling, with his right hand placed over the image of a crucifix on a Bible, the candidate confirmed themselves as not being of either Jewish or Moorish extraction. Then the candidate provided the names of their parents and grandparents, as well as places of birth. Two delegates of the council, church or other public place would then research the information to make sure it was truthful. If the investigation had to be carried out of Cordoba, a person, not necessarily a member of the council, would be appointed to examine the witnesses appointed by the candidate. This researcher would receive a sum per diem according to the rank of the person, the distance traveled and the time spent. Having collected all the reports, the secretary or the notary must read them all to the council and a vote would decide whether the candidate was approved. A simple majority was sufficient, after which the candidate had to promise to obey all the laws and customs of the Church. 
The concept of limpieza de sangre, was a significant barrier for many Spaniards to emigrate to the Americas, since some form of proof of not having recent Moorish or Jewish ancestors was required to emigrate to the Spanish Empire. However, within Spain's overseas territories the concept evolved to be linked with racial purity for both Spaniards and indigenous.  Proofs of racial purity were required in a variety of circumstances in both Spain and its overseas territories. Candidates for office and their spouses had to obtain a certificate of purity that proved that they had no Jewish or Muslim ancestors and in New Spain, proof of whiteness and absence of any in the lineage who engaged in work with their hands. 
Additionally, as early as the sixteenth century, shortly after the Spanish colonization of America was initiated, several regulations were enacted in the Laws of the Indies to prevent Jews and Muslims and their descendants to emigrate and settle in the overseas colonies.  There was a thriving business in creating false documentation to allow conversos to emigrate to Spain's overseas territories.  These provisions banning emigration are repeatedly stressed upon on following editions of the Laws, which provides an indication that the regulations were often ignored,  most likely because colonial authorities at the time looked the other way, as the skills of those immigrants were badly needed. During the period when Portugal and Spain were ruled by the same monarch (1580-1640), Portuguese merchants, many of whom were so-called crypto-Jews (Jews passing as Christians) became important members of the merchant communities in the viceregal capitals of Mexico City and Lima. When Portugal successfully revolted in 1640 from Spain, the Holy Office of the Inquisition in both capitals initiated intensive investigations to identify and prosecute crypto-Jews, resulting in spectacular autos de fe in the mid seventeenth century. 
- Alberro, Solange. Inquisición y sociedad en México, 1571-1700. Mexico City: Fondo de Cultura Económica 1993.
- Beinart, Haim. Conversos ante la inquisición. Jerusalem: Hebrew University 1965.
- Gitlitz, David. Secrecy and Deceit: The Religion of the Crypto-Jews, Albuquerque, NM: University of New Mexico Press, 2002. ISBN 082632813X
- Gojman de Backal, Alicia. "Conversos" in Encyclopedia of Mexico. Chicago: Fitzroy Dearborn 1997, vol. 1, pp. 340–344.
- Gojman Goldberg, Alicia. Los conversos en la Nueva España. Mexico City: Enep-Acatlan, UNAM 1984.
- Greenleaf, Richard E. The Mexican Inquisition in the Sixteenth Century. Albuquerque: University of New Mexico Press 1969.
- Hering Torres, Max S., et al., eds. Race and Blood in the Iberian World. Berlin: Lit, 2012.
- Kamen, Henry. The Spanish Inquisition. London: Weidenfeld and Nicolson 1965.
- Lafaye, Jacques. Cruzadas y Utopias: El judeocristianismo en las sociedades Ibéricas. Mexico City: Fondo de Cultura Económica 1984.
- Lanning, John Tate. "Legitimacy and Limpieza de Sangre in the Practice of Medicine in the Spanish Empire." Jahrbuch für Geschicte 4 (1967)
- Liebman, Seymour. Los Judíos en México y en América Central. Mexico city: Siglo XXI 1971.
- Martínez, Maria Elena. "Limpieza de Sangre" in Encyclopedia of Mexico, vol. 1, pp. 749-752. chicago: Fitzroy Dearborn 1997.
- Roth, Norman, Conversos, Inquisition, and the Expulsion of the Jews from Spain, Madison, WI: University of Wisconsin Press, 1995. ISBN 0299142302
- Seed, Patricia. To Love, Honor, and Obey in Colonial Mexico: Conflicts over Marriage Choices, 1574-1821. Stanford: Stanford University Press 1988.
- Sicroff, Albert A. Los estatutos de limpieza de sangre. Translated by Mauro Armiño. Madrid: Tauros 1985.
- Estatutos de Limpieza de Sangre, Pablo A. Chami.
- Maria Elena Martínrez, Genealogical Fictions: Limpieza de sangre, religion, and gender in colonial Mexico. Stanford, Calif: Stanford University Press 2008.
- Manuel de Larramendi, Corografía de la muy noble y muy leal provincia de Guipúzcoa, Bilbao, 1986, facsimile edition of that from Editorial Ekin, Buenos Aires, 1950. (Also published by Tellechea Idígoras, San Sebastián, 1969.) Quoted in La idea de España entre los vascos de la Edad Moderna, by Jon Arrieta Alberdi, Anales 1997-1998, Real Sociedad Económica Valenciana de Amigos del País.
- Limpieza de sangre in the Spanish-language Auñamendi Encyclopedia
- Aranzadi, Juan (7 March 2012). Milenarismo vasco: Edad de Oro, etnia y nativismo. Penguin Random House Grupo Editorial España. pp. 508–509. ISBN 978-84-306-1581-0.
- Codigos Españoles Tome X. Page 225
- Colección Legislativa de España (1870), p. 364
- Colección Legislativa de España (1870), page 365
- Colección Legislativa de España (1870), page 366
- Los judíos en España, Joseph Pérez. Marcial Pons. Madrid (2005).
- Sicroff, Albert A. Los estatutos de Limpieza de Sangre. p. 121.
- Maria Elena Martinez, Genealogical Fictions: Limpieza de Sangre, Religion, and Gender in Colonial Mexico. Stanford: Stanford University Press 2008, p. 270.
- Martinez, Genealogical Fictions, p. 273.
- Maria Elena Martínez, "Limpieza de Sangre" in Encyclopedia of Mexico, vol. 1, p. 751. Chicago: Fitzroy Dearborn 1997.
- Alicia Gojman de Backal, "Conversos" in Encyclopedia of Mexico, Chicago: Fitzroy Dearborn 1997, vol. 1, p.341.
- Avrum Ehrlich, Mark (2009). Encyclopedia of the Jewish diaspora: origins, experiences, and culture. ABC-CLIO. p. 689. ISBN 1-85109-873-9.
- Jonathan I. Israel, Race, Class, and Politics in Colonial Mexico, 1610-1670. Oxford: Oxford University Press 1975, p. 245-46.
- Attestment of the purity of blood of Justo Rufino de San Martín (brother of José) in Paredes de Nava, 1794. Note - Google translation from Spanish to English.
- Douglass, William A. (2004) Sabino's sin: racism and the founding of Basque nationalism in Daniele Conversi (ed.), Ethnonationalism in the Contemporary World. London: Routledge, pp. 95–112.
- Códigos Españoles Concordados y Anotados Tomo Décimo. Calle Jesús del Valle #6, Madrid; Google Books: M. Rivadeneyra. 1850.
- Colección legislativa de España: Continuación de la colección de decretos (Primer Semestre de 1870) (Tomo CIII). Madrid; Google Books: Ministerio de Gracia y Justicia. 1870.