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.