The Juan Orrego-Salas Legacy Collection consists of published and manuscript scores of Orrego-Salas's music, as well as letters to and from Orrego-Salas, photographs, concert programs, and writings by and about Orrego-Salas.
Within the scores portion of the collection are hundreds of items, covering 145 specific works, as well as several sketches of unknown and unfinished works. Orrego-Salas’s output spans a wide range of genres and instrumentations, from orchestral music, including symphonies and concertos, chamber music, and works for solo instruments, to choral and vocal works such as oratorios, cantatas, and operas, as well as music for film, theatre, ballet, and popular music ensembles. Orrego-Salas's compositional career covers over 70 years, beginning with Romance del establo de Belén and Dos piezas para violin y piano, op. 1 in 1936 and ending with Estancias del recuerdo, op. 127 in 2007.