Contemporary Classical Music (1975—present)

Belongs to the period that started in the mid-1970s with the retreat of modernism. However, the term may also be employed in a broader sense to refer to all post-1945 modern musical forms. Some of the contemporary composers (Cage, Cowell, Glass, Reich) represented a new methodology of experimental music, which began to question fundamental notions of music such as notation, performance, duration, and repetition, while others (Babbitt, Rochberg, Sessions) fashioned their own extensions of the twelve-tone serialism of Arnold Schoenberg.

Source: http://en.wikipedia.org/wiki/Contemporary_classical_music