The Herbert Spencer Jennings Papers contain at least 17 volumes of diaries and various other workbooks, notebooks, and commonplace books with which researchers may supplement those volumes. Although the volumes span 1903-1945, Jennings maintains them most regularly between 1924-1945, providing detailed insights into his research, teaching, professional networks, writing and publications in the fields of microbiology, genetics, and, to a lesser degree, eugenics. For a short period (1924-27) he maintains some entries in shorthand, but returns to a long form thereafter. Integrated throughout his entries are occasional pieces of ephemera, including notes from students (e.g. 4/8/1929), business cards (11/4/1931), newspaper clippings (7/31/1933), and even the passport photos for he and his wife, Mary Louise Spencer (6/27/1935). Researchers interested in his biography, may choose to begin their research using the volume dated 3/11/1938, which contains entries as late as 1/1/1945. That volume encompasses his retirement from Johns Hopkins University (1938), the death of his first wife, Mary (also in 1938), and his remarriage to Lulu Plant Jennings (1939). Jennings' extended trips abroad, including Italy (1903-4), Japan (1931-33), and England (1933-36), may interest scholars researching twentieth-century Europe. Notably, he maintained separate notebooks with further records and ephemera related to both of the latter trips, including two notebooks related to Japanese language and two large scrapbooks related to his time at Oxford. Finally, scholars specifically interested in his career may take an interest in his sporadic notes concerning eugenics (e.g. 1/27/1933) and Charles Davenport, who also maintained an extensive set of diaries available at the APS (Mss.B.D27). For example, nested inside the diary dated 10/12/1928-7/10/1929, Jennings encloses a note addressed to a Mrs. Lutz (5/31/1929), in which he congratulates her on the twenty-fifth anniversary of an institute, which is almost certainly Davenport's Carnegie Institute (opened 6/11/1904).