The evolution of the role of the trombone as a solo instrument in the nineteenth and twentieth centuries can be traced most effectively through four schools of playing, with the music of today's avant-garde being a logical historical culmination of these four schools. It will be demons t rated that the avant-garde's use of the solo trombone has merely continued the evolutionary process started in the early nineteenth century. The contribution of the early nineteenth-century virtuosi was the establishment of the idea that the trombone could compete on its own terms with other instruments as a solo instrument. In addition to expanding the technical capabilities, they also left a basic solo repertoire. With the death of the virtuosi the trombone as a solo instrument went into a decline. For the remainder of the nineteenth century and well into the twentieth century the Paris Conservatoire was influential. Standards of solo performance were brought to new heights by excellent study material and contest solos. The next important step came from the late nineteenth-century American band virtuosi. Their influence helped the public to accept the idea of the trombone as a solo instrument. The American jazz trombonists of the 1930's and 1940's also further widened the technical capabilities of the trombone and also further encouraged acceptance of the Instrument in its solo capacity. However, their most important contribution was in new tonal colors. The music of the avant-garde takes all these previous historical achievements and makes use of them in its own unique way.