Limpieza de sangre in the context of Gitanos

The Expulsion of the Jews from Spain, formalized by the Alhambra Decree of March 31, 1492, was a royal edict issued by the Catholic Monarchs Ferdinand II of Aragon and Isabella I of Castile ordering all unconverted Jews to leave their kingdoms and territories by the end of July that year, unless they converted to Christianity. Motivated by a desire for religious unity following the completion of the Reconquista and amid fears that unconverted Jews were influencing conversos (Jewish converts to Christianity) to revert to Judaism, the decree brought to an end more than a millennium of Jewish presence in the Iberian Peninsula. It also ranks among the most consequential events in Spanish and Jewish history.

In the decades before 1492, successive crises had already thinned Spain's Jewish population through violence, forced conversion, and legal discrimination. In the aftermath of the 1391 massacres, large numbers of Jews converted to Catholicism. Continued attacks produced about 50,000 additional conversions by 1415. Authorities suspected that some conversos continued to practice Judaism in secret; concerns over such "Judaizing" helped motivate the creation of the Spanish Inquisition in 1478, which investigated cases of heresy and, in some instances, used torture and imposed penalties up to execution for the unrepentant. Growing limpieza de sangre ("purity-of-blood") statutes in the 15th century further stigmatized "New Christians" of Jewish descent.

The history of the Jews in the current-day Spanish territory stretches back to Biblical times according to Jewish tradition, but the settlement of organised Jewish communities in the Iberian Peninsula possibly traces back to the times after the destruction of the Second Temple in 70 CE. The earliest archaeological evidence of Hebrew presence in Iberia consists of a 2nd-century gravestone found in Mérida. From the late 6th century onward, following the Visigothic monarchs' conversion from Arianism to the Nicene Creed, conditions for Jews in Iberia considerably worsened.

After the Umayyad conquest of Hispania in the early 8th century, Jews lived under the Dhimmi system and progressively Arabised. Jews of Al-Andalus stood out particularly during the 10th and the 11th centuries, in the caliphal and first taifa periods. Scientific and philological study of the Hebrew Bible began, and secular poetry was written in Hebrew for the first time. After the Almoravid and Almohad invasions, many Jews fled to Northern Africa and the Christian Iberian kingdoms. Targets of antisemitic mob violence, Jews living in the Christian kingdoms faced persecution throughout the 14th century, leading to the 1391 pogroms. As a result of the Alhambra Decree of 1492, the remaining practising Jews in Castile and Aragon were forced to convert to Catholicism (thus becoming 'New Christians' who faced discrimination under the limpieza de sangre system) whereas those who continued to practise Judaism (c. 100,000–200,000) were expelled, creating diaspora communities. Tracing back to a 1924 decree, there have been initiatives to favour the return of Sephardi Jews to Spain by facilitating Spanish citizenship on the basis of demonstrated ancestry.

Old Christian (Spanish: cristiano viejo, Portuguese: cristão-velho, Catalan: cristià vell) was a social and law-effective category used in the Iberian Peninsula from the late 15th and early 16th century onwards, to distinguish Portuguese and Spanish people attested as having cleanliness of blood, known as Limpieza de sangre, from the populations categorized as New Christian. 'New Christian' refer to mainly persons of partial or full Jewish descent who converted to Christianity, and their descendants.

After the expulsion of the Jewish population from Spain in 1492, and Portugal in 1497, all the Jewish population in Iberia became officially Christian. The New Christians were always under suspicion of apostasy. The creation of the Spanish Inquisition in 1478 and the Portuguese Inquisition in 1536 was justified by the need to fight heresy. It was believed that many New Christians were practicing their original religion in secret and large numbers were Crypto-Jews. The term was thus introduced in order for "Old Christians" to distinguish themselves from the converts (conversos), and their descendants, who were seen as potential heretics and threats to Catholic orthodoxy. New Christians of Muslim heritage were referred to pejoratively as moriscos, meaning Moor-like. Those of Jewish heritage were termed marranos (swine, pigs).