in music, auxiliary part or parts of a composition designed to support the principal part or to throw it into relief. In secular medieval music and in much folk and non-European music, instrumental accompaniments for singers consist of unison or octave duplications of the melody (sometimes with slight differences, creating heterophony, the simultaneous performance of variant versions of the same melody), of novel rhythmic features, or of a drone (sustained note or notes) played on wind or stringed instruments. In 16th-century European music, solo songs were sung with simple lute accompaniments, both chordal and contrapuntal (using interwoven melodic lines); notable examples include the songs of the English composer John Dowland and the French airs de cour (courtly songs or airs).

The beginning of the 17th century saw the introduction of the thorough bass (basso continuo), or basso continuo, a type of harmonic accompaniment improvised at the harpsichord or organ and based on chords that the composer indicated by figures. By the 18th century, thorough bass accompaniments designed to support either a soloist, as in the sonatas and solo cantatas of J.S. Bach, or an instrumental ensemble, as in the operas of the Italian composer Alessandro Scarlatti, demanded from the performer a high degree of ornamental and contrapuntal invention. The accompaniment thus assumed a role as important as that of the soloist.

The term obbligato accompaniment came to be applied to accompaniments of this type, as opposed to ad libitum accompaniment, the unessential ornamentation or the optional reduplication of a part, performed on a secondary instrument. Obbligato accompaniments were sometimes written out, among them one originally improvised by Bach for a movement of his Sonata in B Minor for flute and harpsichord. In the second half of the 18th century the obbligato accompaniment assumed a primary role, gaining increased complexity and musical substance while the solo instrument was reduced to the role of an ad libitum accompaniment. Thus, Mozart followed the example of a contemporary composer, Johann Schobert, in writing four sonatas for harpsichord accompanied by the violin.

The influence of the obbligato style of the late 18th century is suggested in Beethoven's statement “I came into the world with obbligato accompaniment.” Obbligato style persisted into the 19th century in both solo and concerted works of the Romantic composers, in which accompaniments became even more elaborate and expressive. The expressive resources of the piano allowed the accompaniments of Schubert to illustrate pictorial or psychological aspects of the texts of his lieder (“songs”). His example was followed in the lieder of Schumann, Brahms, and Hugo Wolf. Piano accompaniments in works for string or wind instruments acquired the status of a concerted part. Orchestral accompaniment was greatly developed in the Romantic concerto and in songs and song cycles with orchestra by numerous composers from Hector Berlioz (1803–69) to Alban Berg (1885–1935) and Benjamin Britten (1913–76).

The art of piano accompaniment flourished chiefly in response to the demands in the 19th century of the German lied and the French mélodie. Qualities of poetic and musical insight and also of ensemble playing distinguish the piano accompanist's art, which resembles the art of performance in chamber music. In the 20th century, accompanists such as the English pianist Gerald Moore and the Dutch pianist Coenraad Valentyn Bos developed the art by their sensitive attitude to the soloist and by their power to interpret the composer's intention.