Harry Partch in the context of Prelude (music)

Experimental music is a general label for any music or music genre that pushes existing boundaries and genre definitions. Experimental compositional practice is defined broadly by exploratory sensibilities radically opposed to, and questioning of, institutionalized compositional, performing, and aesthetic conventions in music. Elements of experimental music include indeterminacy, in which the composer introduces the elements of chance or unpredictability with regard to either the composition or its performance. Artists may approach a hybrid of disparate styles or incorporate unorthodox and unique elements.

The practice became prominent in the mid-20th century, particularly in Europe and North America. John Cage was one of the earliest composers to use the term and one of experimental music's primary innovators, utilizing indeterminacy techniques and seeking unknown outcomes. In France, as early as 1953, Pierre Schaeffer had begun using the term musique expérimentale to describe compositional activities that incorporated tape music, musique concrète, and elektronische Musik. In America, a quite distinct sense of the term was used in the late 1950s to describe computer-controlled composition associated with composers such as Lejaren Hiller. Harry Partch and Ivor Darreg worked with other tuning scales based on the physical laws for harmonic music. For this music they both developed a group of experimental musical instruments. Musique concrète is a form of electroacoustic music that utilises acousmatic sound as a compositional resource. Free improvisation or free music is improvised music without any rules beyond the taste or inclination of the musician(s) involved; in many cases, the musicians make an active effort to avoid clichés; i.e., overt references to recognizable musical conventions or genres.

An experimental musical instrument (or custom-made instrument) is a musical instrument that modifies or extends an existing instrument or class of instruments, or defines or creates a new class of instrument. Some are created through simple modifications, such as cracked cymbals or metal objects inserted between piano strings in a prepared piano. Some experimental instruments are created from household items like a homemade mute for brass instruments such as bathtub plugs. Other experimental instruments are created from electronic spare parts, or by mixing acoustic instruments with electric components.

The instruments created by the earliest 20th-century builders of experimental musical instruments, such as Luigi Russolo (1885–1947),Harry Partch (1901–1974), and John Cage (1912–1992), were not well received by the public at the time of their invention. Even mid-20th century builders such as Ivor Darreg, Pierre Schaeffer and Pierre Henry did not gain a great deal of popularity. However, by the 1980s and 1990s, experimental musical instruments gained a wider audience when they were used by bands such as Einstürzende Neubauten and Neptune.

In music theory, limits or harmonic limits are a way of characterizing the harmony found in a piece or genre of music, or the harmonies that can be made using a particular scale. The term limit was introduced by Harry Partch, who used it to give an upper bound on the complexity of harmony, hence the name.

Lou Silver Harrison (May 14, 1917 – February 2, 2003) was an American composer, music critic, music theorist, painter, and creator of unique musical instruments. Harrison initially wrote in a dissonant, ultramodernist style similar to his former teacher and contemporary, Henry Cowell, but later moved toward incorporating elements of non-Western cultures into his work. Notable examples include a number of pieces written for Javanese style gamelan instruments, inspired after his introduction to noted gamelan musician Kanjeng Notoprojo. Harrison would create his own musical ensembles and instruments with his partner, William Colvig, who are now both considered founders of the American gamelan movement and world music; along with composers Harry Partch and Claude Vivier, and ethnomusicologist Colin McPhee.

The majority of Harrison's works and custom instruments are written for just intonation rather than the more widespread equal temperament, making him one of the most prominent composers to have experimented with microtones. He was also one of the first composers to have written in the international language Esperanto, and among the first to incorporate strong themes of homosexuality in his music.