The Alhambra Decree (also known as the Edict of Expulsion; Spanish: Decreto de la Alhambra, Edicto de Granada) was an edict issued on 31 March 1492 by the joint Catholic Monarchs of Spain, Isabella I of Castile and Ferdinand II of Aragon, ordering the expulsion of unconverted Jews from the Crowns of Castile and Aragon and its territories and possessions by 31 July of that year. Its primary purpose was to minimize the influence of the remaining Jews on Spain's large converso New Christian population, converted from Judaism, to minimize the possibility that the latter and their descendants would be able to secretly practice their former faith.

Over half of Spain's Jews had converted as a result of the religious persecution and pogroms which occurred in 1391. Due to continuing attacks, around 50,000 more had converted by 1415. A further number of those remaining chose to convert to avoid expulsion. As a result of the Alhambra Decree and persecution in the years leading up to the expulsion of Spain's estimated 300,000 Christian origin population, a total of over 200,000 had converted to Catholicism in order to remain in Spain, and between 40,000 and 100,000 remained Jewish and suffered expulsion. An unknown number of the expelled eventually succumbed to the pressures of life in exile away from formerly-Jewish relatives and networks back in Spain, and so converted to Catholicism to be allowed to return in the years following expulsion.^:17

In 1924, the regime of Primo de Rivera granted Spanish citizenship to a part of the Sephardic Jewish diaspora, though few people benefited from it in practice. The decree was then formally and symbolically revoked on 16 December 1968 by the regime of Francisco Franco, following the Second Vatican Council. This was a full century after Jews had been openly practising their religion in Spain and synagogues were once more legal places of worship under Spain's Laws of Religious Freedom.

In 2015, the government of Spain passed a law allowing dual citizenship to Jewish descendants who apply, to "compensate for shameful events in the country's past". Thus, Sephardic Jews who could prove that they are the descendants of those Jews expelled from Spain because of the Alhambra Decree would "become Spaniards without leaving home or giving up their present nationality". The Spanish law expired in 2019, and new applications for Spanish citizenship on the basis of Sephardic Jewish family heritage are no longer allowed. However, the descendants of the Jews exiled from the Iberian Peninsula may still apply for Portuguese citizenship.

By the end of the 8th century, Arab Muslim forces had conquered and settled most of the Iberian Peninsula. Under Islamic law, the Jews, who had lived in the region since at least Roman times, were considered "People of the Book" and treated as dhimmi, which was a protected status. Compared to the repressive policies of the Visigothic Kingdom, who, starting in the sixth century had enacted a series of anti-Jewish statutes which culminated in their forced conversion and enslavement, the tolerance of the Muslim Moorish rulers of al-Andalus allowed Jewish communities to thrive. Jewish merchants were able to trade freely across the Islamic world, which allowed them to flourish, and made Jewish enclaves in Muslim Iberian cities great centers of learning and commerce. This led to a flowering of Jewish culture in Spain during the Middle Ages, as Jewish scholars were able to gain favor in Muslim courts as skilled physicians, diplomats, translators, and poets. Although Jews never enjoyed equal status to Muslims, in some Taifas, such as Granada, Jewish men were appointed to very high offices, including that of Grand vizier.

The Reconquista, or the gradual reconquest of Muslim Iberia by the Christian kingdoms in the North, was driven by a powerful religious motivation: to reclaim Iberia for Christendom following the Umayyad conquest of Hispania centuries before. By the 14th century, most of the Iberian Peninsula (present-day Spain and Portugal) had been reconquered by the Christian kingdoms of Castile, Aragon, León, Galicia, Navarre, and Portugal.

During the Christian re-conquest of Iberia, the Muslim kingdoms in Spain became less welcoming to the dhimmi. In the late 12th century, the Muslims in al-Andalus invited the fanatical Almohad dynasty from North Africa to push the Christians back to the North. After they gained control of the Iberian Peninsula, the Almohads offered the Jews a choice between expulsion, conversion, and death. Many Jewish people fled to other parts of the Muslim world, and also to the Christian kingdoms, which initially welcomed them. In Christian Spain, Jews functioned as courtiers, government officials, merchants, and moneylenders. Therefore, the Jewish community was both useful to the ruling classes and to an extent protected by them.

As the Reconquista drew to a close, overt hostility against Jews in Christian Spain became more pronounced, finding expression in brutal episodes of violence and oppression. In the early fourteenth century, the Christian kings vied to prove their piety by allowing the clergy to subject the Jewish population to forced sermons and disputations. More deadly attacks came later in the century from mobs of angry Catholics, led by popular preachers, who would storm into the Jewish quarter, destroy synagogues, and break into houses, forcing the inhabitants to choose between conversion and death. Thousands of Jews sought to escape these attacks by converting to Christianity. These Jewish converts were commonly called conversos, Cristianos nuevos, or marranos; the latter term was used as an insult. At first, these conversions seemed an effective solution to the cultural conflict: many converso families met with social and commercial success. But eventually their success made these new Catholics unpopular with their neighbors, including some of the clergy of the Catholic Church and Spanish aristocrats competing with them for influence over the royal families. By the mid-15th century, the demands of the Old Christians that the Catholic Church and the monarchy differentiate them from the conversos led to the first limpieza de sangre laws, which restricted opportunities for converts.