Grand opera is a genre of 19th-century opera generally in four or five acts, characterized by large-scale casts and orchestras. The original productions consisted of spectacular design and stage effects with plots normally based on or around dramatic historic events. The term is particularly applied (sometimes specifically used in its French-language equivalent grand opéra, pronounced [ɡʁɑ̃t‿ɔpeʁa]) to certain productions of the Paris Opéra from the late 1820s to around 1860; 'grand opéra' has sometimes been used to denote the Paris Opéra itself.

The term 'grand opera' is also used in a broader application in respect of contemporary or later works of similar monumental proportions from France, Germany, Italy, and other countries.

It may also be used colloquially in an imprecise sense to refer to 'serious opera without spoken dialogue'.

Paris at the turn of the 19th century was a magnet for composers, both French and foreign, especially those of opera. The term "grand opéra" became current in the early 19th century, with contemporaries like the critic Castil-Blaze defining it as a work that was sung throughout (in contrast to opéra comique), performed at the prestigious Paris Opéra, and had a noble subject. The librettist Étienne de Jouy further advocated for a five-act structure and plots drawn from heroic historical events. The aesthetic goals of the Empire were exemplified by works like Gaspare Spontini's Fernand Cortez (1809), which combined an exotic setting with melodramatic plots and spectacular tableaux, such as a cavalry charge and the burning of an Aztec temple. These large-scale works were the immediate forerunners of grand opéra. Other factors contributing to Parisian supremacy in operatic spectacle were the Opéra's ability to stage sizeable productions, its long tradition of French ballet, and its skilled staff of innovative designers like Duponchel, Cicéri, and Daguerre. The first theater performance lit by gas, for example, was Aladin ou La lampe merveilleuse at the Opéra in 1823.

Several operas by Spontini, Luigi Cherubini, and Gioachino Rossini can be regarded as direct precursors to the genre. These include Spontini's La vestale (1807) and Fernand Cortez (1809), Cherubini's Les Abencérages (1813), and Rossini's Le siège de Corinthe (1827) and Moïse et Pharaon (1828). All of these have the characteristics of size and spectacle that would become hallmarks of grand opéra. An especially important forerunner was Giacomo Meyerbeer's Il crociato in Egitto (1824). Produced by Rossini in Paris in 1825, this opera successfully blended the Italian vocal style with German orchestral techniques, introducing a wider range of musical-theatrical effects than traditional Italian opera. With its exotic historical setting, on-stage bands, and themes of culture clash, Il crociato exhibited many of the features that would form the basis of grand opera's popularity.

What became the essential features of 'grand opéra' were foreseen by Étienne de Jouy, the librettist of Guillaume Tell, in an essay of 1826:

Division into five acts seems to me the most suitable for any opera that would reunite the elements of the genre: [...] where the dramatic focus was combined with the marvellous: where the nature and majesty of the subject [...] demanded the addition of attractive festivities and splendid civil and religious ceremonies to the natural flow of the action, and consequently needed frequent scene changes.

The first opera of the grand opera canon is, by common consent, Daniel Auber's La muette de Portici (1828). This tale of a revolution set in Naples in 1647, which culminates in an eruption of Mount Vesuvius into which the heroine throws herself, embodied the musical and scenic sensationalism that would become the genre's hallmark. The libretto for La muette was by Eugène Scribe, a dominant force in French theater who specialized in melodramatic and historical plots. Scribe's first libretto for the Opéra, it was so well-suited to the public taste that he went on to write or be associated with many of the most successful grand operas that followed. La muette's reputation was further cemented by its being the catalyst for a genuine revolution when it was performed in Brussels in 1830.