Twelve-tone music is a compositional technique developed by composer Arnold Schoenberg in the early 20th century. It uses a specific series of the twelve pitches of the chromatic scale, ensuring that each note is treated equally and avoiding traditional tonal hierarchies. This series, or "tone row," can be manipulated through various methods, such as inversion and retrograde, to create different musical ideas. The twelve-tone method marked a significant shift in Western classical music, moving away from the established rules of harmony and melody. Composers like Alban Berg and Anton Webern further explored this technique, contributing to the development of serialism and influencing modern music across various genres.