The collection consists of articles, correspondence, course notes, scrapbooks (1937-1952), memorabilia, and printed matter of Mendel, a professor of music at Princeton (1952-1973). The collection contains correspondence between Mendel, professional colleagues, and organizations such as the American Musicological Society, the Josquin Committee, and the International Josquin Festival Conference (June 1971) in New York, N.Y. There are also Mendel's records on the status of dissertations, course notes for a senior seminar in music history, material on pitches of various instruments and standard tuning frequencies, and scrapbooks containing letters, public relations announcements, and newspaper reviews of the Cantata Singers of All Souls Church in New York City, of which he was the conductor. In addition, there are liability insurance policies and cancelled personal checks of Mendel's wife, Elsa.

Additional material, also unprocessed was added to the collection in May 2007. This material includes sixteen binders and folders of Mendel while he was at Princeton University. The binders contain sheet music, original manuscript material, class curriculum and notes, and writings and criticism of Bach. Also included is correspondence; a binder labeled "Arthur's Honors"; photographs from an exhibition about Mendel; personal photographs; a photo album of his wife Elsa Wissell and her family, and documents about her death and her estate; photographs and letters about the "Cantata Singers"; printed material; and newspaper clippings.