* Atonality: The absence of a tonal center, or key.
* Polyrhythms: The use of multiple rhythms simultaneously.
* Polyharmony: The use of multiple harmonies simultaneously.
* Sound masses: The use of dense clusters of notes.
* Extended techniques: The use of unconventional playing techniques, such as plucking the strings of a piano with a metal rod.
* Indeterminacy: The use of chance or aleatory elements in composition.
* Electronic music: The use of electronic instruments and sounds.