20th-century classical music is art music that was written between the years 1901 and 2000, inclusive. Musical style diverged during the 20th century as it never had previously, so this century was without a dominant style. Modernism, impressionism, and post-romanticism can all be traced to the decades before the turn of the 20th century, but can be included because they evolved beyond the musical boundaries of the 19th-century styles that were part of the earlier common practice period. Neoclassicism and expressionism came mostly after 1900. Minimalism started much later in the century and can be seen as a change from the modern to postmodern era, although some date postmodernism from as early as about 1930. Aleatory, atonality, serialism, musique concrète, electronic music, and concept music were all developed during the century. Jazz and ethnic folk music became important influences on many composers during this century.

Neoclassicism in music was a twentieth-century trend, particularly current in the interwar period, in which composers sought to return to aesthetic precepts associated with the broadly defined concept of "classicism", namely order, balance, clarity, economy, and emotional restraint. As such, neoclassicism was a reaction against the unrestrained emotionalism and perceived formlessness of late Romanticism, as well as a "call to order" after the experimental ferment of the first two decades of the twentieth century. The neoclassical impulse found its expression in such features as the use of pared-down performing forces, an emphasis on rhythm and on contrapuntal texture, an updated or expanded tonal harmony, and a concentration on absolute music as opposed to Romantic program music.