Professionalization in public health reflects wider institutional and political forces. Depending on the historical context in different countries, public health has developed as a medical specialty or as an independent field, entirely within the state or in mixed public-private institutions, closely or weakly tied to social movements, and in varying relations to fields such as engineering, nursing, environmental science, and the military. In early 20th-century America, the rise of the medical profession and the biomedical model of disease had a formative influence on public health, leading to a different institutional pattern from Britain. Public health in the United States emerged (1) largely outside the medical profession, but under the sway of the biomedical model; (2) without medicine's command of an exclusive jurisdiction and high status; and (3) with a limited role in healthcare organization and planning. Professionalism in public health continues to be subjected to contradictory pressures and uncertainties. Healthcare reform, bioterrorism, and environmental crises could expand its mandate and access to resources, but conflicts with other institutions are likely to result in limits on the capacity of public health professionals to assert an exclusive jurisdiction.