Serialism
Schoenberg was not the only composer to use this way of composing.  His pupils Alban Berg (1885-1935) and Anton Webern (1883-1945) also wrote twelve-tone music. Schoenberg, Webern & Berg are sometimes called the "Second Viennese School"-The first was Haydn, Mozart and Beethoven a hundred years before. The composers Igor Stravinsky (1882-1971) and Aaron Copland (1900-1990) started to write twelve-tone music when they were quite old.  Composers such as Benjamin Britten (1913-1976) used it occasionally, often putting it together with music which was tonal (listen to Britten’s opera “Midsummer Night’s Dream”).  When contrasted with tonal music in this way it can be very beautiful.