in music, an instrumental form characterized by the initial statement and subsequent restatement of a particular melody or section, the various statements of which are separated by contrasting material.

Although any piece built upon this basic plan of alternation or digression and return may be legitimately designated rondo, most rondos conform to one of two basic schemes: the five-part (abaca, with a representing the main theme) and the seven-part (abacaba). The latter is symmetrically balanced, since two essentially ternary (ternary form) aba sections are separated by a contrasting and often extended, if not always developing, c section.

In another form of rondo, the seven-part scheme may not be symmetrical: the second a section sometimes develops and modulates as it merges with the c section, as in the so-called sonata-rondo form. In the clearest examples of sonata-rondo movements, the second ab forms the recapitulation of the initial ab, and the second b remains in the principal key.

The rondo was a particularly popular musical structure during the last half of the 18th and the early 19th centuries, when it frequently formed the final movement in sonatas (a famous instance is the "Rondo alla turca" 【“Rondo in Turkish style”】 in Wolfgang Amadeus Mozart (Mozart, Wolfgang Amadeus)'s Sonata for piano K 331), symphonies (notably those of Joseph Haydn (Haydn, Joseph)), chamber works, and especially concerti (notably Mozart's); it was sometimes used in operas as well. The rondo form also appears in some 18th- and 19th-century slow movements, as in Franz Schubert's Symphony No. 9 in C Major (1828). During the same period, the rondo enjoyed a certain vogue as a separate composition. Well-known examples include Mozart's Rondo in A Minor for piano, K 511 (1787), and his remarkable “Scene with Rondo” for soprano and orchestra with piano, K 505; Ludwig van Beethoven (Beethoven, Ludwig van)'s Two Rondos, Opus 51 (c. 1796–98), and Rondo a capriccio (also known as Rage Over a Lost Penny), Opus 129 (1795); Frédéric Chopin's Krakowiak for piano and orchestra (1828); and Richard Strauss's Till Eulenspiegel's Merry Pranks (1894–95) for orchestra, a rondo that is programmatic (i.e., depicting an extramusical idea).

The Classical rondo seems to have developed from the keyboard rondeau of the French Baroque, where a refrain of 8 or 16 measures is played in alternation with a succession of couplets (episodes) so as to form a chainlike structure of variable length: abacad, etc. A favourite example of rondeau is François Couperin's Les baricades mistérieuses, from his Pièces de clavecin, Book 2 (1716–17; “Harpsichord Pieces”). This form in turn is related to the rondeau form in medieval poetry.