The Mosque–Cathedral of Córdoba (Spanish: Mezquita-Catedral de Córdoba [meθˈkita kateˈðɾal de ˈkoɾðoβa]) is the cathedral of the Roman Catholic Diocese of Córdoba in the Spanish region of Andalusia. Officially called the Cathedral of Our Lady of the Assumption (Spanish: Catedral de Nuestra Señora de la Asunción), it is dedicated to the Assumption of Mary. Due to its status as a former mosque, it is also known as the Mezquita (Spanish for 'mosque') and, in a historical sense, as the Great Mosque of Córdoba.

According to traditional accounts, a Visigothic church, the Catholic Christian Basilica of Vincent of Saragossa, originally stood on the site of the current Mosque-Cathedral, although this has been a matter of scholarly debate. The Great Mosque was constructed in 785 on the orders of Abd al-Rahman I, founder of the Islamic Emirate of Córdoba. It was expanded multiple times afterwards under Abd al-Rahman's successors up to the late 10th century. Among the most notable additions, Abd al-Rahman III added a minaret (finished in 958), and his son al-Hakam II added a richly decorated new mihrab and maqsurah section (finished in 971). The mosque was converted to a cathedral in 1236 when Córdoba was captured by the Christian forces of Castile during the Reconquista. The structure itself underwent only minor modifications until a major building project in the 16th century inserted a new Renaissance cathedral nave and transept into the center of the building. The former minaret, which had been converted to a bell tower, was also significantly remodelled around this time. Starting in the 19th century, modern restorations have, in turn, led to the recovery and study of some of the building's Islamic-era elements. Today, the building continues to serve as the city's cathedral, and Mass is celebrated there daily.

The mosque structure is an important monument in the history of Islamic architecture and was highly influential on the subsequent "Moorish" architecture of the western Mediterranean regions of the Muslim world. It is also one of Spain's major historic monuments and tourist attractions, as well as a UNESCO World Heritage Site since 1984.

A claim that the site of the mosque-cathedral was once a Roman temple dedicated to Janus dates as far back as Pablo de Céspedes and is sometimes still repeated today. However, Robert Knapp, in his 1983 study of Roman-era Córdoba, dismissed this claim as speculation based on a misunderstanding of Roman milestones found in the area.

According to traditional accounts, the present-day site of the Cathedral–Mosque of Córdoba was originally a Visigothic Christian church dedicated to Saint Vincent of Saragossa, which was divided and shared by Christians and Muslims after the Umayyad conquest of Hispania. As the Muslim community grew and this existing space became too small for prayer, the basilica was expanded little by little through piecemeal additions to the building. This sharing arrangement of the site lasted until 785, when the Christian half was purchased by Abd al-Rahman I, for a hundred thousand dinars. He then demolished the church structure and built the new mosque on its site. In return, Abd al-Rahman also allowed the Christians to build or rebuild some churches outside the city walls. These included churches dedicated to the Christian martyrs Saints Faustus, Januarius, and Marcellus whom they deeply revered.^{[better source needed]}

The historicity of this narrative has been challenged as archaeological evidence is scant and the narrative is not corroborated by contemporary accounts of the events following Abd al-Rahman I's initial arrival in al-Andalus. The narrative of the church being transformed into a mosque, which goes back to the tenth-century historian Al-Razi, echoed similar narratives of the Islamic conquest of Syria, in particular the story of building the Umayyad Mosque in Damascus. For medieval Muslim historians, these parallels served to highlight a dynastic Umayyad conquest of Spain and appropriation of Visigothic Córdoba. Another tenth-century source mentions a church that stood at the site of the mosque without giving further details. An archaeological exhibit in the mosque–cathedral of Cordoba today displays fragments of a Late Roman or Visigothic building, emphasizing an originally Christian nature of the complex. The "stratigraphy" of the site is complicated and made more so by the impact of contemporary political debates about cultural identity in Spain.

According to Susana Calvo Capilla, a specialist on the history of the mosque–cathedral, although remains of multiple church-like buildings have been located on the territory of the mosque–cathedral complex, no clear archaeological evidence has been found of where either the church of St. Vincent or the first mosque were located on the site, and the latter may have been a newly constructed building. The evidence suggests that it may have been the grounds of an episcopal complex rather than a particular church which were initially divided between Muslims and Christians. Pedro Marfil, an archeologist at the University of Cordoba, has argued for the existence of such a complex – including a Christian basilica – on this site by interpreting the existing archeological remains. D. Fairchild Ruggles, a scholar of Islamic art, considers previous archeological work to be a confirmation of the former church's existence. This theory has been opposed by Fernando Arce-Sainz, another archeologist, who states that none of the numerous archeological investigations in modern times have turned up remains of Christian iconography, a cemetery, or other evidence that would support the existence of a church. Art historian Rose Walker, in an overview of late antique and early medieval art in Spain, has likewise criticized Marfil's view as relying on personal interpretation. More recently, archeologists Alberto León and Raimundo Ortiz Urbano have affirmed the hypothesis of a large episcopal complex by analyzing both old and new archeological findings at the site, while María de los Ángeles Utrero Agudo and Alejandro Villa del Castillo argue that evidence so far does not allow for the identification of former ecclesiastical structures on the site.

Regardless of what structures may have existed on the site, however, it is almost certain that the building which housed the city's first mosque was destroyed to build Abd ar-Rahman I's Great Mosque and that it had little relation to the latter's form.