One of the styles that evolved after the 12-tone, dissonant, academic counterpoint of the early and middle 20th century was Minimalism. It was pioneered by LaMont Young, Terry Riley, Steve Reich, and Philip Glass. They embraced repetitive, rhythmic music with layers of independent lines and a high degree of stasis. Many notable composers expanded Minimalist concepts, including John C. Adams and Louis Andriessen.
See also 16th & 17th Century Concert, 18th & 19th Centuries, 20th Century Concert, 20th & 21st Century Popular.