The Alcázar de los Reyes Cristianos (Spanish for "Castle of the Christian Monarchs"), also known as the Alcázar of Córdoba, is a medieval Alcázar located in the historic centre of Córdoba, Spain, next to the Guadalquivir River and near the Grand Mosque. The Alcázar takes its name (Arabic: القصر‎, translit. Al-Qasr, lit. 'The Palace'‎). The fortress served as one of the primary residences of Isabella I of Castile and Ferdinand II of Aragon.

In early medieval times, the site was occupied by a Visigoth fortress. When the Visigoths fell to the Umayyad conquest of Hispania, the emirs of the Umayyad Caliphate in Damascus rebuilt the structure. The Umayyads fell to the Abbasid Caliphate and the surviving member of the Umayyad Dynasty, Abd ar-Rahman I, fled to Córdoba. Abd ar-Rahman I's successors established the independent Caliphate of Córdoba and used the Alcázar as their palace. The city subsequently flourished as an important political and cultural center, and the Alcázar was expanded to a very large compound with baths, gardens, and the largest library in the West. Watermills on the nearby Guadalquivir powered water lifting to irrigate the extensive gardens.

In 1236, Christian forces took Córdoba during the Reconquista. In 1328, Alfonso XI of Castile began building the present day structure on part of the site for the old fortress. Other parts of the Moorish Alcázar had been given as spoils to the bishop, nobles, and the Order of Calatrava. Alfonso's structure retained only part of the Moorish ruins but the structure appears Islamic since Alfonso used the Mudéjar style.

The Alcázar was involved in the civil war where Henry IV of Castile faced a rebellion that backed his teenage half-brother Alfonso. During the war, the Alcázar's defenses were upgraded to deal with the advent of gunpowder. At the same time, the Alcázar's main tower, now known as the "Inquisition Tower" was constructed.

Henry's successor, Isabella and her husband Ferdinand used the Alcázar for one of the first permanent tribunals of the Spanish Inquisition and as a headquarters for their campaign against the Nasrid dynasty in Granada, the last remaining Moorish kingdom in the Iberian Peninsula. The Inquisition began using the Alcázar as one of its headquarters in 1482, converting much of it, including the Arab baths, into torture and interrogation chambers. The Inquisition maintained a tribunal here for three centuries. Boabdil was held prisoner here in 1483 until he promised to make Granada a tributary state. When Boabdil refused to surrender his kingdom in 1489, the Christians launched an attack. Isabella and Ferdinand's campaign against Granada succeeded in 1492. The same year, the monarchs met Christopher Columbus in the Alcázar as he prepared to take his first voyage to the Americas.

The Alcázar served as a garrison for Napoleon Bonaparte's troops in 1810. In 1821, the Alcázar became a prison. Finally, the Spanish government made the Alcázar a tourist attraction and national monument in the 1950s.

The Alcázar centers on the Patio Morisco ("Courtyard of the Moriscos"), another popular feature. There are two towers: the Torre de los Leones ("Tower of the Lions) and the Torre de Homenaje ("Tower of Homage"). The latter has Gothic features including an ogival ceiling.

A series of Roman mosaics and a Roman sarcophagus are displayed in the Inquisition Tower.