Broadly speaking, chamber music is any ensemble music suited to a small room rather than to a large concert hall. Listeners may find themselves better attuned to the subtleties of musical dialogue occurring between the four members of a string quartet if they are hearing the music in a museum gallery rather than in a cavernous space with 5,000 seats. Since much of the instrumental music from the era of noble patronage (roughly 1500 to 1800) was written for performance in a room of a palace or estate, various forms of Renaissance and Baroque instrumental music, from dance pieces of Henry VIII's time to the violin sonatas of Corelli, might qualify as chamber music.
More strictly, the term "chamber music" refers to music for small ensembles written during the era of the symphony orchestra — from about 1760 to the present. The most characteristic chamber genre is the string quartet (two violins, viola, and cello), perfected by Franz Joseph Haydn in the second half of the eighteenth century. Other chamber music ensembles include the piano trio (violin, cello, and piano), the piano quintet (string quartet plus piano), and other groupings ranging from two to eight or nine musicians. Chamber works in general are often classified according to the number of players involved, as duos, trios, quintets, and so on. Mozart's string quartets were heavily influenced by Haydn's example, and he even dedicated a set of quartets to the older composer. The string quartets of Beethoven are evenly distributed over his entire career, and the last five, often referred to as his "late quartets," share the mystic quality of profound joy that many hear in the composer's Symphony No. 9. The duo sonata, for solo instrument with piano accompaniment, has been a primary household genre since the late eighteenth century and has spawned concert masterpieces like Beethoven's Violin Sonata No. 10 in G major, Op. 96.
Romantic radicals like Berlioz, Liszt, and Wagner had no use for chamber music and its restrained tone; the chamber music of the Romantic era came mostly from composers who extended the forms they inherited from Mozart and Beethoven. The piano quintet, uniting the string quartet with the quintessential Romantic instrument, proved a popular combination; magnificent examples came from Schubert (the "Trout" Quintet), Schumann, and Dvorák. Perhaps the greatest nineteenth-century composer of chamber music was Brahms, whose depth of musical thought influenced even his most experimental successors.
Chamber music experienced something of a resurgence in the twentieth century, perhaps because composers who were making each piece of music into a miniature sound world of its own wanted a medium that would display what they were doing with maximum clarity. Much of the slender output of Anton Webern, one of the early adopters of the abstract 12-tone method, consists of works for small ensemble. From the six perfectly rendered string quartets of Béla Bartók to the Eastern philosophico-musical world of Japanese composer Toru Takemitsu and beyond, modern composers have often worked on a small canvas. Among the most energetic promoters of chamber music in the present day has been the San Francisco-based Kronos Quartet, which has commissioned numerous new works, and more new works are written today for chamber ensembles than for orchestra or the stage.