In the two to three decades that followed World War Two, approximately three-quarters of all New Zealand doctors, and up to ninety per cent of New Zealand medical specialists, travelled overseas for the purposes of obtaining post-graduate experience and qualifications. This thesis uses oral interviews, quantification techniques, and a range of textual analyses to explore the form and function of this large-scale professional migration, and to capture the experiences of those doctors who participated in it. The central argument of this thesis is that the careers of New Zealand specialists during this period cannot be understood without making reference to a complex and mutually influential international system of cultural and professional conventions, institutional rules, interpersonal networks, health related policies, and discursive formations. While powerfully centred on British medical norms and structures, this ‘Common-health’ system facilitated the transmission of people, ideas, technologies, and policies both within and between the nations of the British Commonwealth, in multiple directions by multiple means, and in doing so, was critical to the development of medical specialisation in the twentieth century. For New Zealand’s prospective specialists, the primary motivating force behind these migrations was the need to access populations that were large enough to facilitate specialist training. Britain’s much larger population and the existence of a range of cultural and institutional commonalities, derived from nineteenth-century colonisation, made Britain the default destination for thousands of New Zealand trainee specialists during the second half of the twentieth century. However, while the Common-health system was a powerful facilitator of medical interaction and migration, it also functioned as a mechanism of exclusion that severely curtailed the ability of women doctors and those of non-European heritage to participate in professional medicine on their own terms. This thesis examines this restrictive aspect of post-World War Two medical networks with relation to women by suggesting that traditional beliefs about the role of women in medicine, together with the strongly informal nature of many professional interactions, not only limited the overall participation of women doctors, but also conditioned their ability to access particular specialty fields. The thesis also examines the reconfiguration of these patterns of connection during the late 1960s and early 1970s, and in particular, the emergence of the United States and Australia as important venues for post-graduate training for New Zealand’s prospective specialists.