Petrushka (ballet) in the context of Tamara Karsavina

Igor Fyodorovich Stravinsky (17 June [O.S. 5 June] 1882 – 6 April 1971) was a Russian composer and conductor with French citizenship (from 1934) and American citizenship (from 1945). He is widely considered one of the most important and influential composers of the 20th century and a pivotal figure in modernist music.

Born to a musical family in Saint Petersburg, Russia, Stravinsky grew up taking piano and music theory lessons. While studying law at the University of Saint Petersburg, he met Nikolai Rimsky-Korsakov and studied music under him until the latter's death in 1908. Stravinsky met the impresario Sergei Diaghilev soon after, who commissioned the composer to write three ballets for the Ballets Russes's Paris seasons: The Firebird (1910), Petrushka (1911), and The Rite of Spring (1913), the last of which caused a near-riot at the premiere due to its avant-garde nature and later changed the way composers understood rhythmic structure.

The Firebird (French: L'Oiseau de feu; Russian: Жар-птица, romanized: Zhar-ptitsa) is a ballet and orchestral concert work by the Russian composer Igor Stravinsky. It was written for the 1910 Paris season of Sergei Diaghilev's Ballets Russes company; the original choreography was by Michel Fokine, who collaborated with Alexandre Benois and others on a scenario based on the Russian fairy tales of the Firebird and the blessing and curse it possesses for its owner. It was first performed at the Opéra de Paris on 25 June 1910 and was an immediate success, catapulting Stravinsky to international fame and leading to future Diaghilev–Stravinsky collaborations including Petrushka (1911) and The Rite of Spring (1913).

The Firebird's mortal and supernatural elements are distinguished with a system of leitmotifs placed in the harmony dubbed "leit-harmony". Stravinsky intentionally used many specialist techniques in the orchestra, including ponticello, col legno, flautando, glissando, and flutter-tonguing. Set in the evil immortal Koschei's castle, the ballet follows Prince Ivan, who battles Koschei with the help of the magical Firebird.

The Rite of Spring (French: Le Sacre du printemps) is a ballet and orchestral concert work by the Russian composer Igor Stravinsky. It was written for the 1913 Paris season of Sergei Diaghilev's Ballets Russes company; the original choreography was by Vaslav Nijinsky with stage designs and costumes by Nicholas Roerich. When first performed at the Théâtre des Champs-Élysées on 29 May 1913, the avant-garde nature of the music and choreography caused a sensation. Many have called the first-night reaction a "riot" or "near-riot", though this wording did not come about until reviews of later performances in 1924, over a decade later. Although designed as a work for the stage, with specific passages accompanying characters and action, the music achieved equal if not greater recognition as a concert piece and is widely considered to be one of the most influential musical works of the 20th century.

Stravinsky was a young, virtually unknown composer when Diaghilev recruited him to create works for the Ballets Russes. Le Sacre du printemps was the third such major project, after the acclaimed Firebird (1910) and Petrushka (1911). The concept behind The Rite of Spring, developed by Roerich from Stravinsky's outline idea, is suggested by its subtitle, "Pictures of Pagan Russia in Two Parts"; the scenario depicts various primitive rituals celebrating the advent of spring, after which a young girl is chosen as a sacrificial victim and dances herself to death. After a mixed critical reception for its original run and a short London tour, the ballet was not performed again until the 1920s, when a version choreographed by Léonide Massine replaced Nijinsky's original, which saw only eight performances. Massine's was the forerunner of many innovative productions directed by the world's leading choreographers, gaining the work worldwide acceptance. In the 1980s, Nijinsky's original choreography, long believed lost, was reconstructed by the Joffrey Ballet in Los Angeles.

Polytonality (also polyharmony) is the musical use of more than one key simultaneously. Bitonality is the use of only two different keys at the same time. Polyvalence or polyvalency is the use of more than one harmonic function, from the same key, at the same time.

Some examples of bitonality superimpose fully harmonized sections of music in different keys.