Isang Yun (윤이상, born September 17, 1917 in Chungmu [now Tongyeong, South Korea; died November 3, 1995 in Berlin) was a Korean-German composer. Yun's primary musical concern was the development of Korean music through Western musical means. After experimenting with 12-tone techniques during his studies at Darmstadt, Yun developed his own musical personality in his works of the early 1960s. Yun's music employed techniques associated with traditional Korean music, such as glissandi, pizzicati and vibrati. Also central to his style was the presence of multiple-melodic lines, which Yun called Haupttöne ("principal" or "main tones").

Yun began writing music at the age of 14, and began formally studying music two years later at the Osaka Conservatory, before taking composition classes under Tomojiro Ikenouchi in Tokyo from 1938. After Japan entered World War II, he moved back to Korea and participated in the Korean independence movement. He was captured and imprisoned by the Japanese in 1943.

After the war, he did welfare work, establishing an orphanage for war orphans, and teaching music in Tongyeong and Busan. After the armistice ceasing hostilities in the Korean War in 1953, he began teaching at the Seoul National University. He received the Seoul City Culture Award in 1955, and traveled to Europe the following year to finish his musical studies.

In Paris and West Berlin, he studied contemporary music under Pierre Revel, Boris Blacher, Josef Rufer, and Reinhard Schwarz-Schilling. He attended the International Summer Courses of Contemporary Music in Darmstadt, and began his career in Europe with premieres of his Five Pieces for Piano and Music for Seven Instruments. His music was recognized for its fusion of East Asian and Western classical musical traditions. The premiere of his oratorio Om mani padme hum in 1965 and Réak in 1966 gave him international renown.

He first visited North Korea in 1963, and returned there several times after 1979, and promoted the idea of a joint concert featuring musicians from both Koreas, which finally took place in 1990. Yun settled in West Berlin in 1964, and, in 1967, became involved in the East Berlin spy incident. On June 17, he was kidnapped by the South Korean secret police, along with his wife I Soo-ja and many Korean students in West Berlin. He was taken to Seoul, condemned for espionage and sentenced to life imprisonment. A worldwide petition led by Igor Stravinsky and Herbert von Karajan was presented to the South Korean government, signed by approximately 200 artists, including Luigi Dallapiccola, Hans Werner Henze, Heinz Holliger, Mauricio Kagel, Joseph Keilberth, Otto Klemperer, György Ligeti, Arne Mellnas, Per Nørgård, and Karlheinz Stockhausen. Yun I-sang was released and exiled in 1969, returning to West Berlin. He was not allowed to visit South Korea again.

He taught at the Hanover Academy of Music for a year, and was Professor of Composition at the Hochschule der Künste in West Berlin from 1970 to 1985. He obtained German citizenship in 1971. From 1973 he began participating in organizations and conferences in Japan and the United States calling for the democratization of South Korea, and the reunification of the country.

In 1984, the Isang Yun Music Institute opened in Pyongyang, North Korea. Yun was invited to attend a festival of his music in South Korea in 1994, but the trip was broken off after conflict with the government. On 3 November 1995, Yun died of pneumonia in Berlin. The International Isang Yun Society was founded in Berlin in 1996.

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