Don Carlos is a five-act grand opera composed by Giuseppe Verdi to a French-language libretto by Joseph Méry and Camille du Locle, based on the dramatic play Don Carlos, Infant von Spanien (Don Carlos, Infante of Spain) by Friedrich Schiller. In addition, it has been noted by David Kimball that the Fontainebleau scene and auto da fé "were the most substantial of several incidents borrowed from a contemporary play on Philip II by Eugène Cormon".

Given its premiere at the Salle Le Peletier on 11 March 1867, the opera's story is based on conflicts in the life of Carlos, Prince of Asturias (1545–1568), after his betrothed Elisabeth of Valois was married instead to his father Philip II of Spain as part of the peace treaty ending the Italian War of 1551–1559 between the Houses of Habsburg and Valois. It was commissioned and produced by the Théâtre Impérial de l'Opéra (Paris Opera).

When performed in one of its several Italian versions, the opera is generally called Don Carlo. The first Italian version given in Italy was in Bologna in March 1867. Revised again by Verdi, it was given in Naples in November/December 1872. Finally, two other versions were prepared: the first was seen in Milan in January 1884 (in which the four acts were based on some original French text which was then translated). It is now known as the "Milan version". The second, also sanctioned by the composer, was the "Modena version" and presented in that city in December 1886. It added the "Fontainebleau" first act to the Milan four-act version.

Over the following twenty years, cuts and additions were made to the opera, resulting in a number of versions being available to directors and conductors. No other Verdi opera exists in so many versions. At its full length (including the ballet and the cuts made before the first performance), it contains about four hours of music and is Verdi's longest opera.