The events of three periods occurring during 1900 1980 are traced to illustrate the sources from which forensic serology evolved. The growth of blood grouping and blood transfusion, especially during the periods of military exigency, comprise the basic structure of forensic serology. Chaotic serologic procedures and confusing A-B-O terminology presented multiple challenges to workers in the field, including hospital transfusion services. The 1940s saw a beginning of standardization achieved through a combination of training, research and recommendations of the National Research Council to the Armed Services.