This collection contains correspondence, manuscripts, opera librettos, songs, short stories, novels, sketches, and critical reviews. It also has personal family papers of Kurt (Ashley Vernon) and Greta Hartwig Manschinger, paintings and writings by and other records from Greta's sister Mela Hartwig and her husband Robert Spira, audio recordings, scores, and sheet music, as well as audio recordings of performances.

Julius Rudel (1921-2014) was an opera and orchestra conductor who graduated from the Mannes School of Music in 1942. He served as music director for several organizations, most notably as director and principal conductor for New York City Opera from 1957 to 1979. The collection includes annotated conducting scores, notes, a scrapbook of news clippings, programs and playbills, correspondence, biographical material, and photographs.

This collection documents the musical career of Yella Pessl, a harpsichordist, pianist and organist.

The collection contains approximately 1300 scores, half of which bear markings entered by Mikhashoff or his colleagues in preparation for performance. The collection includes manuscripts and print publications, both originals and reproductions.