Duke of Medinaceli is an hereditary title in the peerage of Spain, accompanied by the dignity of Grandee. The Catholic Monarchs, Ferdinand II of Aragon and Isabella I of Castile, created the title and awarded it on 31 October 1479 to Luis de la Cerda y de la Vega. He also held the title of 5th Count of Medinaceli, which was first awarded in 1368 to his ancestor, Bernal de Foix.

The Spanish nobility are people who possess a title of nobility confirmed by the Spanish Ministry of the Presidency, Justice and Relations with the Cortes, as well as those individuals appointed to one of Spain's three highest orders of knighthood, the Order of the Golden Fleece, the Order of Charles III and the Order of Isabella the Catholic. Some member of the Spanish nobility possess various titles that may be inherited or not, but the creation and recognition of titles is legally the prerogative of the Monarchy of Spain.