Lou Silver Harrison (May 14, 1917 – February 2, 2003) was an American composer, music critic, music theorist, painter, and creator of unique musical instruments. Harrison initially wrote in a dissonant, ultramodernist style similar to his former teacher and contemporary, Henry Cowell, but later moved toward incorporating elements of non-Western cultures into his work. Notable examples include a number of pieces written for Javanese style gamelan instruments, inspired after his introduction to noted gamelan musician Kanjeng Notoprojo. Harrison would create his own musical ensembles and instruments with his partner, William Colvig, who are now both considered founders of the American gamelan movement and world music; along with composers Harry Partch and Claude Vivier, and ethnomusicologist Colin McPhee.

The majority of Harrison's works and custom instruments are written for just intonation rather than the more widespread equal temperament, making him one of the most prominent composers to have experimented with microtones. He was also one of the first composers to have written in the international language Esperanto, and among the first to incorporate strong themes of homosexuality in his music.

Harrison was born on May 14, 1917, in Portland, Oregon, to parents Clarence "Pop" Harrison and former Alaska resident Calline Lillian "Cal" Harrison (née Silver). The family was initially well-off financially from past inheritances, but fell on hard times leading up to the Great Depression. Harrison lived in the Portland area for only nine years before moving with his parents and younger brother, Bill, to a number of locations in Northern California, including Sacramento, Stockton, and finally, San Francisco. With the city having a large population of Asian Americans at the time, Harrison was often surrounded by the influence of the East. His mother decorated their home with Japanese lanterns, ornate Persian rugs, and replicas of ancient Chinese artifacts. The diverse array of music he was exposed to there, including Cantonese opera, Hawai'ian kīkākila, jazz, norteño and classical music, deeply fascinated and interested him. He would later say he had heard far more traditional Chinese music than European music by the time he was an adult.

Harrison's early interest in music was supported by his parents, with Cal paying for occasional piano lessons and Pop driving the young Harrison to study traditional Gregorian chant at the Mission San Francisco de Asís for a short period. The family's frequent moves in search of work, however, provided the adolescent Harrison little opportunity to develop any long-term friendships. Often feeling like an outsider, he relied on his own judgment to guide his aesthetic decisions and decidedly drifted further and further away from the artistic style of the West. He instead retreated into furthering his own personal education, often spending time at the local library to read books on everything ranging from zoology to Confucianism. He recalled being able to read two books a day, and the extremely wide diaspora of interests prompted him to connect disparate influences throughout his life, including in his future compositions. It's believed the loneliness of his youth contributed to his strong dislike of urban metropolises and so-called "city life".

Harrison discovered he was gay while attending Burlingame High School and realizing his attraction toward a male classmate. By the time he graduated in December 1934 at the age of 17, he had come out to his family, and decided thereafter to make no attempt at hiding his sexual preference and personality – nearly unheard of for gay men of the time.

After graduating high school in 1934, Harrison enrolled in San Francisco State College (now San Francisco State University). It was there where he took Henry Cowell's "Music of the Peoples of the World" course being offered by the UC Berkeley Extension. Harrison quickly became one of Cowell's most enthusiastic students, and he subsequently appointed him as class assistant. After attending a Palo Alto performance of one of Cowell's pieces for piano and improvised percussion in June 1935, Harrison would proclaim it to be one of the most extraordinary works he had ever heard. He would later incorporate similar elements of found percussion and aleatoric performance in his music. In fall of the same year, Harrison approached Cowell for private composition lessons, initiating a personal and professional friendship that continued until Cowell's death from cancer in 1965. He was the first to publish Harrison's music, through the publishing house he founded, New Music Edition. During Cowell's four-year stay in San Quentin Prison on a morals charge involving homosexual acts, Harrison publicly appealed for his release, and regularly visited him for composition lessons through the prison's bars.

While still studying at age 19, he became an interim professor of music at Mills College in Oakland from 1936 to 1939. In 1941, he transferred to the University of California, Los Angeles to work in the dance department; teaching students Laban movement analysis and playing piano accompaniment. While there, he took theory lessons from Arnold Schoenberg, leading him to further his interest in the infamous twelve-tone technique. He would later say, "... it was no jump at all to learn to write twelve-tone music; Henry's the one who taught me." The pieces he was writing at this time, however, were largely percussive works using unconventional materials, such as discarded car brake drums and garbage cans, as musical instruments. Few of his surviving pieces – including one of the earliest known examples, Prelude for Grandpiano (1937) – follow the serialist twelve-tone idiom. He began using tone clusters in his piano works, à la Cowell, but differed from his technique by calling for an "octave bar" – a flat wooden bar approximately an octave long, with a slightly concave rubber bottom. This allowed the clusters to be much louder than they otherwise would be, and gave the piano more of an unpitched, gong-like sound. His experimental and free-wheeling style flourished during this period, with pieces like the Concerto for Violin and Percussion Orchestra (1940) and Labyrinth (1941). This ultramodern and avant-garde music captured the attention of John Cage, another one of Cowell's students. Harrison and Cage would collaborate in the years following, and engage in several romantic liaisons.

Harrison was recommended several times to study musical composition in Paris – or Europe more broadly – but resolved several times against it, due to his staunch position of promoting and elevating the status of his fellow American composers. In 1943, Harrison moved to New York City and worked as a music critic for the Herald Tribune at the behest of fellow composer and tutor Virgil Thomson. While there, he met and befriended many modernist composers of the East Coast, including Carl Ruggles, Alan Hovhaness, and most consequentially, Charles Ives. Harrison would later dedicate himself to bringing Ives to the attention of the musical world – whose works had largely been scoffed at or ignored up to that point. With the assistance of his mentor Cowell, he engraved and conducted the premiere of Ives's Symphony No. 3 (1910); receiving financial help from Ives in return. When Ives won the Pulitzer Prize for Music for that piece, he gave half of the money rewarded to Harrison. Harrison also edited a large number of Ives's works, receiving compensation often in excess of what he billed.