Papers, letters, memoranda, memorabilia, and manuscript music scores assembled by and related to the life and musical activities of Anton Seidl. The collection includes many letters from Cosima Wagner and her children addressed to Anton Seidl and his wife, the opera singer Auguste Kraus Seidl. There are also letters from Lilli Lehman, Edvard Grieg, Antonin Dvorak, Bronislaw Hubermann, Carl Goldmark, Maud Powell, Marianne Brandt, Felix Weingartner, Lyman Abbott, and many others. The letters are chiefly concerned with musical performances, composition, and related affairs. There are journals, diaries, and memoranda in Seidl's hand, as well as photographs and clippings relating to his conducting career. Also, twenty-seven manuscript scores of Seidl's orchestrations of various works.

Letters, notes, programs, photographs, and printed materials. The collection is comprised primarily of handwritten correspondence between Reiner and notable music figures including Samuel Barber, Leonard Bernstein, Aaron Copland, Lukas Foss, Darius Milhaud, Arthur Nikisch. Arnold Schoenberg, Richard Strauss, Igor Stravinsky, and Leo Weiner. Also of note, letters from writer and conductor Gian Francesco Milpiero and his wife Auna detailing wartime conditions in Italy (1946).

Letters of musical composers and performers such as George Gershwin, Douglas Moore, Arnold Schönberg, Arturo Toscanini, Maria Cherubini, Jacques Halévy (F. Halévy), and Gaspare Spontini.