Imperator totius Hispaniae is a Latin title meaning "Emperor of All Spain". In Spain in the Middle Ages, the title "emperor" was used under a variety of circumstances from the ninth century onwards, but its usage peaked, as a formal and practical title, between 1086 and 1157. It was primarily used by the kings of León and Castile, but it also found currency in the Kingdom of Navarre and was employed by the counts of Castile and at least one duke of Galicia. It signalled at various points the king's equality with the rulers of the Byzantine Empire and Holy Roman Empire, his rule by conquest or military superiority, his rule over several ethnic or religious groups, and his claim to suzerainty over the other kings of the peninsula, both Christian and Muslim. The use of the imperial title received scant recognition outside of Spain and it had become largely forgotten by the thirteenth century.

The title of imperator originally meant the rough equivalent of commander under the Roman Republic. Later, it became a part of the titulature of the Roman Emperors as their praenomen. The Roman emperors themselves generally based their authority on multiple titles and positions, rather than preferring any single title. Nevertheless, imperator was used relatively consistently as an element of a Roman ruler's title throughout the Principate and the Dominate. The word itself derives from the stem of the verb imperare, meaning 'to order, to command'. The English word emperor derives from imperator via Old French: Empereür.