The authors examined public and published archival documents and interviewed senior and retired Personnel Selection Officers, and influential Industrial/Organisational (I/O) psychologists in Canada to document the history of the Canadian Forces Personnel Selection Branch. The authors highlight the close working relationship between civilian and military I/O psychologists and suggest that they have been mutually influential in shaping the practise of I/O in Canada. Almost every account of the development of Industrial/ Organisational (I/O) in the United States emphasises the formative of the military and military requirements particularly during the World Wars (e.g., Salas, DeRoine, & Gade, 2007). For example, the development of selection instruments during World War I (e.g., Yoakum & Yerkes, 1920) is cited as the catalyst that brought I/O out of the closet of aca- demia (Katzell & Austin, 1992, p. 805) and into the workplace. Similarly, accounts of the development of I/O in the United Kingdom highlight the demands of the military during wartime, as a formative (e.g., Warr, 2007). In contrast, histories of the development of I/O in Canada largely ignore the role of the military (e.g., Latham & Sue-Chan, 1998) or explicitly deny any such influence. Warr (2007, p. 94), for exam- ple, suggests that (c)ontrary to patterns in other countries. World War II . . . did not provide a strong impetus to I-O psychology in Canada. We suggest that this is a substantial understatement of the relationship between military and I/O psychology. In particular, although not very accessible to the civilian reader, partial histories of the Personnel Selection Branch of the Canadian Forces present a dramatically different account (e.g., Anderson, 1992; Eggenberger, 1992; Lamerson, 1995; Northey, 1992; Pinch, 1992; Prociuk, 2001). Our objective in this article was to expand upon these histories and provide a comprehensive account of the relationship between I/O and the Personnel Selection Branch of the Canadian Forces. In doing so, we take the position that such a history is of value in and of itself as documenting the development of one of the largest employers of I/O psychologists in Canada (S. Eyres, per- sonal communication, November 30, 2007). However, we also go beyond this view to suggest that the practise of I/O both shaped, and was influenced by, developments in the Canadian Forces. In doing so, we find evidence for a pattern of spiraling influence in which the personnel demands of the military shape the focus of I/O at some points while at other points advances in I/O led to enhanced personnel practises within the military. It is our hope that reflecting on the past relationship between the Canadian Forces and the profession of I/O will help to foster an appreciation of the mutual benefits of this relationship and help us to understand how this association can be strengthened in the future. We examined public archival documents and interviewed senior and retired Personnel Selection Officers and influential I/O psy- chologists in Canada. We provide a review of the chronological development of the CF Personnel Selection Branch from its offi- cial inception in 1938 to the present, noting the significant events that have contributed to its development during the last 70 years. We conclude by noting the overarching themes and commenting on the reciprocal relationship between the Personnel Selection Branch and the civilian I/O community and how this relationship can continue to be fostered in the future.