information:classification, structural:summarization
Repertoire and performances

Orchestras play a wide range of repertoire ranging from 17th-century dance suites, 18th century divertimentos to 20th-century film scores and 21st-century symphonies. Orchestras have become synonymous with the symphony, an extended musical composition in Western classical music that typically contains multiple movements which provide contrasting keys and tempos. Symphonies are notated in a musical score, which contains all the instrument parts. The conductor uses the score to study the symphony before rehearsals and decide on their interpretation (e.g., tempos, articulation, phrasing, etc.), and to follow the music during rehearsals and concerts, while leading the ensemble. Orchestral musicians play from parts containing just the notated music for their instrument. A small number of symphonies also contain vocal parts (e.g., Beethoven 's Ninth Symphony).

Orchestras also perform overtures, a term originally applied to the instrumental introduction to an opera. During the early Romantic era, composers such as Beethoven and Mendelssohn began to use the term to refer to independent, self-existing instrumental, programmatic works that presaged genres such as the symphonic poem, a form devised by Franz Liszt in several works that began as dramatic overtures. These were "at first undoubtedly intended to be played at the head of a programme". In the 1850s the concert overture began to be supplanted by the symphonic poem.

Orchestras also play with instrumental soloists in concertos. During concertos, the orchestra plays an accompaniment role to the soloist (e.g., a solo violinist or pianist) and, at times, introduces musical themes or interludes while the soloist is not playing. Orchestras also play during operas, ballets, some musical theatre works and some choral works (both sacred works such as Masses and secular works). In operas and ballets, the orchestra accompanies the singers and dancers, respectively, and plays overtures and interludes where the melodies played by the orchestra take centre stage.