This collection contains correspondence, manuscripts, notes, articles, books, ephemera, postcards and black-and-white photographs. Correspondence in Series 1 includes letters from Henri Bergson, Benedetto Croce, F. C. S. Schiller, Arthur Waley and Kimura Hideo, dated 1912-1938. Manuscripts in Series 2 include drafts of Mason's published and unpublished works, as well as letters, contracts, advertisements and notes related to his publications and lectures. Subject files in Series 3 include notes written by Mason and quotes and articles collected by him on various topics in Eastern religions and philosophies. This series also includes miscellaneous notes, "Obras Publicadas," a list of Mason's publications. Photographs in Series 5 and postcards in Series 6 were taken or collected during Mason's stay in Japan in the 1930s (see Related Materials).