Chamber music afforded early 20th-century composers one of the prime areas of musical expression. Composers of chamber music went far in using newly conceived combinations of instruments and voices in their works. The traditional string quartet was still employed, as well as several other classical combinations, but many compositions were written for two to fifteen performers in which not only the standard instruments of all families were combined, but rarely-used instruments were often incorporated. Percussion instruments of all kinds, especially those with tuned bars, were used. The inclusion of the voice in small ensembles was especially characteristic of modern chamber music. The use of these instruments was more than mere exploitation of new and unusual media, it was the use of tone color as a means of formal organization.
The symphony continued as the principal large form for instrumental composition. In the case of some writers, particularly those whose style still favored the Romantic, this form was likely to be extended with colorful orchestration and it often combined voices with the orchestra. At the other extreme were those symphonic writers who reduced the symphony to a mere shadow of its classical self. Serial composers made the most use of this treatment, although a large number of composers wrote music that lay between these extremes and employed many devices to rejuvenate the classical symphonic form.