Correspondence, oral history interview, subject files, family papers, scrapbooks, printed material, photographs, and other papers relating to Simpson's work as a labor and industrial relations expert prior to World War II and to his postwar service as labor attaché in Belgium (1945-1948), Greece (1947-1949), and Mexico (1949-1953) and as deputy consul general in India (1952-1954) and consul general in Mozambique (1954-1957). Subjects include the American peace movement during the post-World War I period, the International Labour Organisation, communist penetration of trade unions in western and southern European countries following World War II, portrayal of labor in the American popular, official, industrial, and trade union press (1945-1954), conduct and history of diplomacy, recruitment and training of Foreign Service officers, and the Georgetown University Institute for the Study of Diplomacy. Family papers concern the genealogy of the Hendree, Simpson, Smith, and Tinsley families. Includes a letter (Jan. 16, 1865) describing the participation of the frigate Wabash in the capture of Fort Fisher in North Carolina during the Civil War.

Family correspondents include Simpson's parents, Hendree P. and Edith Smith Simpson. Other correspondents include Robert W. Bruère, Kenneth W. Colegrove, Marion H. Hedges, Elmo Paul Hohman, Marcel J. Lemmers, Hugh Anderson Moran, Irene H. Moran, Jean Moran, James Thomson Shotwell, William L. Tayler, Florence Calvert Thorne, Oscar Wilder Underwood, Pierre Waelbroeck, Robert J. Watt, Richard Wilson, and John C. Winant.