The collection consists of Don Gillis' compositions and papers, reel-to-reel recordings of many of his compositions and Gillis' discussing his works, and materials related to the series Toscanini: The Man Behind the Legend, which Gillis produced. Gillis' wife Barbara oversaw the donation of this collection, and was a lifelong advocate of Mr.Gillis' work.

Gillis' compositions represent his career from the early 1930s through the 1970s, and include sacred, secular, symphonic, and chamber works. His papers include correspondence, papers related to various projects, schedules, reviews, radio scripts, and the Men of Music radio project, teaching materials, writings, additional papers concerning his work, biographical materials, and newspaper clippings.

The reel-to-reel recordings, 50 in all, contain recordings of Gillis' works and Gillis' own description of them. Transcripts are included in Series 3 of the finding aid.

The recordings of Toscanini: The Man Behind the Legend and The Centennial Series span the years 1963 through 1967, and with few exceptions, each broadcast is linked individually and available for listening through the UNT Digital Library.