Anton Webern in the context of "Hauptstimme"

Atonality in its broadest sense is music that lacks a tonal center, or key. Atonality, in this sense, usually describes compositions written from about the early 20th century to the present day, where a hierarchy of harmonies focusing on a single, central triad is not used, and the notes of the chromatic scale function independently of one another. More narrowly, the term atonality describes music that does not conform to the system of tonal hierarchies that characterized European classical music between the seventeenth and nineteenth centuries. "The repertory of atonal music is characterized by the occurrence of pitches in novel combinations, as well as by the occurrence of familiar pitch combinations in unfamiliar environments".

The term is also occasionally used to describe music that is neither tonal nor serial, especially the pre-twelve-tone music of the Second Viennese School, principally Alban Berg, Arnold Schoenberg, and Anton Webern. However, "as a categorical label, 'atonal' generally means only that the piece is in the Western tradition and is not 'tonal'", although there are longer periods, e.g., medieval, renaissance, and modern modal music to which this definition does not apply. "Serialism arose partly as a means of organizing more coherently the relations used in the pre-serial 'free atonal' music. ... Thus, many useful and crucial insights about even strictly serial music depend only on such basic atonal theory".

The Second Viennese School (German: Zweite Wiener Schule, Neue Wiener Schule) was a group of composers that comprised Arnold Schoenberg and his pupils, particularly Alban Berg and Anton Webern, and close associates in early 20th-century Vienna. Their music was initially characterized by late-Romantic expanded tonality and later, a totally chromatic expressionism without a firm tonal centre, often referred to as atonality; and later still, Schoenberg's serial twelve-tone technique. Using this technique when composing, Schoenberg employed all 12 tones present in Western music's chromatic scale when forming a melody, this melody being the "prime series". This method would later be enhanced in compositions by Schoenberg and his followers through permutations such as "retrogrades", "inversions", "transformations" etc. Later, composers such as Pierre Boulez drew influence from Schoenberg's technique in furthering serialization; serializing not only pitch but rhythm, articulation, and dynamics as well. Theodor Adorno said that the twelve-tone method, when it had evolved into maturity, was a "veritable message in a bottle", addressed to an unknown and uncertain future. Though this common development took place, it neither followed a common time-line nor a cooperative path. Likewise, it was not a direct result of Schoenberg's teaching—which, as his various published textbooks demonstrate, was highly traditional and conservative. Schoenberg's textbooks also reveal that the Second Viennese School spawned not from the development of his serial method, but rather from the influence of his creative example.

Arnold Schoenberg or Schönberg (13 September 1874 – 13 July 1951) was an Austrian and American composer, music theorist, teacher and writer. He was among the first modernists who transformed the practice of harmony in 20th-century classical music, and a central element of his music was its use of motives as a means of coherence. He propounded concepts like developing variation, the emancipation of the dissonance, and the "unity of musical space".

Schoenberg's early works, like Verklärte Nacht (1899), represented a Brahmsian–Wagnerian synthesis on which he built. Mentoring Anton Webern and Alban Berg, he became the central figure of the Second Viennese School. They consorted with visual artists, published in Der Blaue Reiter, and wrote atonal, expressionist music, attracting fame and stirring debate. In his String Quartet No. 2 (1907–1908), Erwartung (1909), and Pierrot lunaire (1912), Schoenberg visited extremes of emotion; in self-portraits he emphasized his intense gaze. While working on Die Jakobsleiter (from 1914) and Moses und Aron (from 1923), Schoenberg confronted popular antisemitism by returning to Judaism and substantially developed his twelve-tone technique. He systematically interrelated all notes of the chromatic scale in his twelve-tone music, often exploiting combinatorial hexachords and sometimes admitting tonal elements.

Contemporary classical music is Western art music composed close to the present day. At the beginning of the 21st century, it commonly referred to the post-1945 post-tonal music after the death of Anton Webern, and included serial music, electronic music, experimental music, and minimalist music. Newer forms of music include spectral music and post-minimalism.

The emancipation of the dissonance was a concept or goal put forth by composer Arnold Schoenberg and others, including his pupil Anton Webern, who styled it The Path to the New Music. The phrase first appears in Schoenberg's 1926 essay "Opinion or Insight?". It may be described as a metanarrative to justify atonality. The musicologist Jim Samson describes:

Henryk Mikołaj Górecki (/ɡəˈrɛtski/ gə-RET-skee; Polish: [ˈxɛnrɨk miˈkɔwaj ɡuˈrɛt͡skʲi] ; 6 December 1933 – 12 November 2010) was a Polish composer of contemporary classical music. According to critic Alex Ross, no recent classical composer has had as much commercial success as Górecki. He became a leading figure of the Polish avant-garde during the post-Stalin cultural thaw. His Anton Webern-influenced serialist works of the 1950s and 1960s were characterized by adherence to dissonant modernism and influenced by Luigi Nono, Karlheinz Stockhausen, Krzysztof Penderecki and Kazimierz Serocki. He continued in this direction throughout the 1960s, but by the mid-1970s had changed to a less complex sacred minimalist sound, exemplified by the transitional Symphony No. 2 and the Symphony No. 3 (Symphony of Sorrowful Songs). This later style developed through several other distinct phases, from such works as his 1979 Beatus Vir, to the 1981 choral hymn Miserere, the 1993 Kleines Requiem für eine Polka and his requiem Good Night.

Górecki was largely unknown outside Poland until the late 1980s. In 1992, 15 years after it was composed, a recording of his Symphony of Sorrowful Songs with soprano Dawn Upshaw and conductor David Zinman became a worldwide commercial and critical success, selling more than a million copies and vastly exceeding the typical lifetime sales of a recording of symphonic music by a 20th-century composer. Commenting on its popularity, Górecki said, "Perhaps people find something they need in this piece of music ... somehow I hit the right note, something they were missing. Something somewhere had been lost to them. I feel that I instinctively knew what they needed." This popular acclaim did not generate wide interest in Górecki's other works, and he pointedly resisted the temptation to repeat earlier success, or compose for commercial reward.