A viceroy () is an official who reigns over a polity in the name of and as the representative of the monarch of the territory. The term derives from the Latin prefix vice-, meaning "in the place of" and the French word roy, meaning "king". He has also been styled the king's lieutenant. A viceroy's territory may be called a viceroyalty, though this term is not always applied. The adjective form is viceregal, less often viceroyal. The term vicereine is sometimes used to indicate a female viceroy suo jure, although viceroy can serve as a gender-neutral term. Vicereine is more commonly used to indicate a viceroy's wife.

The term has occasionally been applied to the governors-general of the Commonwealth realms, who are viceregal representatives of the monarch.

Viceroy is a form of royal appointment rather than noble rank. An individual viceroy often also held a noble title, however, such as Bernardo de Gálvez, 1st Viscount of Galveston, who was also Viceroy of New Spain.