Recently the medical profession has faced increased outside pressure to reform postgraduate medical training programs to better equip young doctors for changing health care needs and public expectations. In this article we explore the impact of reform on professional self-governance by conducting a comparative historical-institutional analysis of postgraduate medical training reform in the United Kingdom and the Netherlands. In both countries the medical training regime has shifted from professional self-regulation to coregulation. Yet there are notable differences in each country that cannot be explained solely by diverging institutional contexts. They also result from the strategic actions by the actors involved. Based on an assessment of the recent literature on institutional transformation, this article shows how strategic actions set negotiating authority processes into motion, producing new and sometimes surprising institutional arrangements that can have profound effects on the distribution and allocation of authority in the medical training regime. It stresses the need to study the interactions among political context, the properties of institutions, and negotiating authority processes, as they are crucially important to understanding institutional transformation.