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.

Correspondence, manuscripts, papers, essays, etc. relating to Berlioz, and 19th century arts and literature. The correspondence includes original Berlioz letters and over 200 copies of letters relating to Berlioz and the romantic era, written by musicians, critics, historians, and literateurs of the past century. There are many photostats of letters and manuscripts obtained from the principal libraries of the world which hold original Berlioz material. The collection includes much printed material in the form of music scores, published letters, essays, clippings, biographies, music and book catalogues, program notes, and playbills.

Correspondence, manuscripts, documents, notes, printed material, and photographs of Leonard Altman concerning his work as editor of LISTEN and board member of Carnegie Hall as well as his other professional and personal interests.