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.

Manuscript materials which include correspondence, business papers, composition scrapbooks and musical scores; books; clippings; records; and photographs.

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.