The Romantic era did not suddenly end in 1900. The years 1890-1910, sometimes called the post-Romantic era, were a musical transition period from the Roamntic era into the twentieth century. During these two decades, a style of music known as Impressionism was popular. Impressionism took its name from the artists who, instead of using clear lines to paint their pictures, used soft images to convey the impression fo a scene. Impressionist composers did the same with music. They used new harmonies, chords, and melodies based on unfamiliar scales or modes to paint a soft musical picture, much like the program music of the Romanitc era.

The main contribution of Impressionist music was the use of new musical harmonies and scales. These harmonies and scales allowed later twentieth century to develop music which was more complex and less rooted in traditional harmonies and melodies. The first style of twentieth century music whcih evolved from Impressionism was known as Neoclassicism, or New Classicism. Neoclassicism was return to musical elements of earlier eras of music, particularly the Baroque and Classical eras. These musical elements became the basis for new compositions using new harmonies, melodies, and rhythms. Neoclassic composers used strict forms, like Classical composers, and much counterpoint, like Baroque composers.

After Impressionism, most composers abandoned the emotionalism and progarm music of the Romantic era and returned to the Classical era concept of music. Other styles that developed include aleatory music or chance music, which is music either composed or performed by chance procedures, such as rolling dice or flipping a coin. Aleatory music sounds differently each time it is performed. It is impossible to predict exactly how it will sound.Serial music is music based on a series of pitches, rhythms, or any musical elements, which are repeated again and again. Atonal music is music without a tonal center. Almost all music composed had a musical key, but atonal music does not. Electronic music is music created by electronic devices. Music created electronically allows the composer to control every aspect of the musical performance.