A viceroy /ˈvaɪs.rɔɪ/ is a royal official who runs a country, colony, or city province (or state) in the name of and as representative of the monarch. The term derives from the Latin prefix vice-, meaning "in the place of" and the French word roi, meaning king. A viceroy's province or larger territory is called a viceroyalty. The adjective form is viceregal, less often viceroyal. A vicereine is a woman in a viceregal position, or a viceroy's wife.

The title was originally used by the Aragonese Crown, where beginning in the 14th century it referred to the governors of Sardinia and Corsica. The absolutist kings of Spain came to appoint numerous viceroys to rule over various parts of their vast Spanish Empire in Europe, the Americas, and overseas elsewhere.

In Europe, until the 18th century the Spanish crown appointed viceroys of Aragon, Valencia, Catalonia, Navarre, Sardinia, Sicily, Naples and Portugal (1580–1640). With the ascension of the House of Bourbon to the Spanish throne, the historic Aragonese viceroyalties were replaced by new Captaincies General. At the end of War of the Spanish Succession, the Spanish Monarchy was shorn of its Italian possessions. These Italian territories, however, continued to have viceroys under their new rulers for some time; Sardinia would have a viceroy until 1848.