The Cook Music Library's primary collection of printed research materials includes more than 750,000 cataloged items. The strengths of the collection include: 19th-century first or early editions of orchestral, chamber, and opera sources; extensive holdings of printed operas; theory treatises; Russian/Soviet music; early keyboard and violin primary source materials (the Willi Apel collections); Black and Latin American music collections; as well as other music special collections of print and audio materials. In addition, the performing ensembles collection contains scores and parts for large ensembles, including virtually all the standard orchestral and choral repertoire in support of the Jacobs School of Music's several choruses and orchestras.

The audio collections contain cataloged sound recordings for use in class assignments, applied music study, and research. The collection is particularly strong in the area of opera, and features among its special collections the Jussi Björling Collection (the world's largest collection of recordings by the Swedish tenor, about 3,000 items), and the Ross Allen and Alvin Ehret collections of vocal recordings (37,000 recordings of operatic and vocal repertoire, including virtually all complete operas recorded between 1950 and 1975, many of them unique or rare in the United States). Special audio collections in jazz are also substantial.

Circulating materials of the Cook Music Library can be searched in IUCAT.