Frequently an opening to a larger dramatic work such as an opera, earlier usage of the word also referred to collections of movements, known as suites. Later works, such as Beethoven's overture Leonora No 3 mark a transition between the concept of overture as introduction to a dramatic entertainment, and musical forms such as the symphonic poem, which are free-standing works in their own right.
The notion of an overture has no existence until the 17th century. The toccata at the beginning of Monteverdi's Orfeo is a barbaric flourish of every procurable instrument, alternating with a melodious section entitled ritornello; and, in so far as this constitutes the first instrumental movement prefixed to an opera, it may be called an overture. As an art-form the overture began to exist in the works of J-B Lully. He devised a scheme which, although he himself did not always adhere to it, constitutes the typical French overture up to the time of Johann Sebastian Bach and George Friderich Handel (whose works have made it classical). This French overture consists of a slow introduction in a marked "dotted rhythm" (i.e. exaggerated iambic, if the first chord is disregarded), followed by a lively movement in fugato style. The slow introduction was always repeated, and sometimes the quick movement concluded by returning to the slow tempo and material, and was also repeated (see Bach's French Overture in the Klavierübung). The operatic French overture was frequently followed by a series of dance tunes before the curtain rose. It thus became used as the prelude to a suite; and the Klavierübung French Overture of Johann Sebastian Bach is a case in point, the overture proper being the introduction to a suite of seven dances. For the same reason Bach's four orchestral suites are called overtures; and, again, the prelude to the fourth partita in the Klavierübung is an overture.
Bach was able to use the French overture form for choruses, and even for the treatment of chorales. Thus the overture, properly so called, of his fourth orchestral suite became the first chorus of the church cantata "Unser Mund so voll Lachens"; the choruses of the cantatas "Preise Jerusalem den Herrn" and "Höchst erwünschtes Freudenfest" are in overture form; and, in the first of the two cantatas entitled "Nun komm der Heiden Heiland", Bach has ingeniously adapted the overture form to the treatment of a chorale.
With the rise of dramatic music and the sonata style, the French overture became unsuitable for opera; and Gluck (whose remarks on the function of overtures in the preface to Alceste are historic) based himself on Italian models, of loose texture, which admit of a sweeping and massively contrasted technique. By the time of Wolfgang Amadeus Mozart's later works the overture in the sonata style had clearly differentiated itself from strictly symphonic music. It consists of a quick movement (with or without a slow introduction), in sonata form, loose in texture, without repeats, frequently without a development section, but sometimes substituting for it a melodious episode in slow time. Instances of this substitution are Mozart's symphony in G, which is an overture to an unknown opera, and his overtures to Die Entführung and to Lo Sposo deluso, in both of which cases the curtain rises at a point which throws a remarkable dramatic light upon the peculiar form. The overture to Figaro was at first intended to have a similar slow middle section, which, however, Mozart struck out as soon as he had begun it. In Beethoven's hands the overture style and form increased its distinction from that of the symphony, but it no longer remained inferior to it; and the final version of the overture to Leonora (that known as No. 3) is the most gigantic single orchestral movement ever based on. the sonata style.
Overtures to plays, such as Ludwig van Beethoven's to Coffin's Coriolan, tend to become detached from their surroundings; and hence arises the concert overture, second only to the symphony in importance as a purely orchestral art-form. Its derivation associates it almost inevitably with external poetic ideas. These, if sufficiently broad, need in no way militate against musical integrity of form; and Felix Mendelssohn's Hebrides overture is as perfect a masterpiece as can be found in any art. The same applies to Brahms's Tragic Overture, one of his greatest orchestral works, for which a more explanatory title would be misleading as well as unnecessary. His Academic Festival Overture is a highly organized working out of German student songs.
In modern opera the overture, Vorspiel, Einleitung, Introduction, or whatever else it may be called, is generally nothing more definite than that portion of the music which takes place before the curtain rises. Tannhäuser is the last case of high importance in which the overture (as originally written) is a really complete instrumental piece prefixed to an opera in tragic and continuous dramatic style. In lighter opera, where sectional forms are still possible, a separable overture is not out of place, though even Carmen is remarkable in the dramatic way in which its overture foreshadows the tragic end and leads directly to the rise of the curtain. Richard Wagner's Vorspiel to Lohengrin is a short self-contained movement founded on the music of the Grail. With all its wonderful instrumentation, romantic beauty and identity with subsequent music in the first and third acts, it does not represent a further departure from the formal classical overture than that shown fifty years earlier by Méhul's interesting overtures to Ariodant and Uthal, in the latter of which a voice is several times heard on the stage before the rise of the curtain.
The Vorspiel to Die Meistersinger, though very enjoyable by itself and needing only an additional tonic chord to bring it to an end, really loses incalculably in refinement by so ending in a concert room. In its proper position its otherwise disproportionate climax leads to the rise of the curtain and the engaging of the listener's mind in a crowd of dramatic and spectacular sensations amply adequate to account for that long introductory instrumental crescendo. The Vorspiel to Tristan has been very beautifully finished for concert use by Wagner himself, and the considerable length and subtlety of the added page shows how little calculated for independent existence the original Vorspiel was. Lastly, the Parsifal Vorspiel is a composition which, though finished for concert use by Wagner in a few extra bars, asserts itself with the utmost lucidity and force as a prelude to some vast design. The orchestral preludes to the four dramas of the Ring owe their whole meaning to their being mere preparations for the rise of the curtain; and these works can no more be said to have overtures than Verdi's Falstaff and Strauss's Salome, in which the curtain rises at the first note of the music.