Articles and reviews, correspondence, broadcast scripts, photographs, and clippings of the Chicago Tribune performing arts critic from 1942 to 1965. Cassidy wrote her influential "On the Aisle" column for the Tribune, then wrote freelance criticism and hosted a weekly program of arts criticism for WFMT, helping to shape the course of music, theater, and dance in Chicago.

Writings and research materials of this music historian. Focused on American opera in the early 1900s, the bulk of the collection concerns the soprano Edith Mason, with some material on composer Hamilton Forrest and soprano Mabel Garrison. Research materials include clippings, photographs and illustrations, correspondence, programs, and other documents.