In 1955, Schuller and jazz pianist John Lewis founded the Modern Jazz Society, which gave its first concert at Town Hall, New York, the same year and later became known as the Jazz and Classical Music Society. While lecturing at Brandeis University in 1957, he coined the term "Third Stream" to describe music that combines classical and jazz techniques. He became an enthusiastic advocate of this style and wrote many works according to its principles, among them Transformation (1957, for jazz ensemble),Concertino (1959, for jazz quartet and orchestra),Abstraction (1959, for nine instruments), and Variants on a Theme of Thelonious Monk (1960, for 13 instruments) utilizing Eric Dolphy and Ornette Coleman. In 1966, he composed the opera The Visitation.
He also orchestrated Scott Joplin's only known surviving opera Treemonisha for the Houston Grand Opera's premiere production of this work in 1975.
In 1959, Schuller gave up performance to devote himself to composition, teaching and writing. He conducted internationally and studied and recorded jazz with such greats as Dizzy Gillespie and John Lewis among many others. Schuller wrote over 190 original compositions in many musical genres.
Schuller recorded the LP Country Fiddle Band with the Conservatory's country fiddle band, released by Columbia Records in 1976. Reviewing in Christgau's Record Guide: Rock Albums of the Seventies (1981), Robert Christgau wrote: "Why do I love this semiclassicized perversion when country fiddle and bluegrass music that strives for authenticity leaves me cold? It's all in the candor of the striving; as usual, I'm put off by the way so-called folk groups formalize a tradition that had spontaneity and unselfconsciousness at the root of its attraction. This silly symphony is something else. The melodies are fetchingly tried-and-true, the (unintentional?) stateliness of the rhythms appropriately nineteenth-century, and the instrumental overkill (twenty-four instruments massed on 'Flop-Eared Mule') both gorgeous and hilarious. A grand novelty."
Schuller was or-in-chief of Jazz Masterworks Editions, and co-director of the Smithsonian Jazz Masterworks Orchestra in Washington, D.C. Another effort of preservation was his ing and posthumous premiering at Lincoln Center in 1989 of Charles Mingus's immense final work, Epitaph, subsequently released on Columbia/Sony Records. He was the author of two major books on the history of jazz, Early Jazz (1968) and The Swing Era (1991).
From 1993 until his death, Schuller served as Artistic Director for the Northwest Bach Festival in Spokane, Washington state. Each year the festival showcased works by J.S. Bach and other composers in venues around Spokane. At the 2010 festival, Schuller conducted the Mass in B minor at St. John's Cathedral, sung by the chamber choir from Eastern Washington University, accompanied by the Spokane Symphony. Other notable performances conducted at the festival include the St Matthew Passion in 2008 and Handel's Messiah in 2005.
Schuller's association with Spokane began with guest conducting the Spokane Symphony for one week in 1982. He then served as Music Director from 1984–1985 and later regularly appeared as a guest conductor. Schuller also served as Artistic Director to the nearby Festival at Sandpoint.
His modernist orchestral work Where the Word Ends, organized in four movements corresponding to those of a symphony, premiered at the Boston Symphony Orchestra in 2009.
In 2011 Schuller published the first volume of a two-volume autobiography, Gunther Schuller: A Life in Pursuit of Music and Beauty.
In 2012, Schuller premiered a new arrangement, the Treemonishasuite from Joplin's opera. It was performed as part of The Rest is Noise season at London's South Bank in 2013.
Schuller died on June 21, 2015 in Boston, from complications from leukemia. He married Marjorie Black, a singer and pianist, in 1948. Their marriage produced two sons, George and Edwin, and lasted until her death in 1992. His sons survive him, as does his brother Edgar.
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^Babbitt, Gunther Schuller ; foreword by Milton (1999). Musings : the musical worlds of Gunther Schuller : a collection of his writings (1st Da Capo Press ed.). New York: Da Capo Press. ISBN9780306809026.
^Carlos do Nascimento Silva, Luiz (2000). Put your dreams away : a Frank Sinatra discography (1. publ. ed.). Westport, Conn. [u.a.]: Greenwood Press. ISBN0313310556.
^Lambert, Philip (2013). Alec Wilder. Urbana: University of Illinois Press. p. 63. ISBN9780252094842.
^Silver, Horace (2006). Let's Get to the Nitty Gritty: The autobiography of Horace Silver. Berkeley, Calif. [u.a.]: University of California Press. p. 211. ISBN9780520243743.
^Summers, Claude (2004). The Queer Encyclopedia of Music, Dance & Musical Theater (1st ed.). San Francisco: Cleis Press. pp. 165–166. ISBN9781573441988.