De facto policy on the public's health in the United States is overwhelmingly biomedical, to the near exclusion of non-biomedical approaches and institutions. Environmental health and protection are particularly marginal within the modern public health policy system, despite growing awareness of the significance of the environment to public health. This was not always the case. Early policy on the public's health was dominated by environmental approaches and institutions. While the rise of medicine and biomedical research is well known, the historic relationship of biomedicine to environmental approaches within a public health policy context has been less examined. This dissertation seeks to understand why this transition happened and how policy makers justified and institutionalized this change in policy. This dissertation looks at the political discourse and rhetoric surrounding several key pieces of federal legislation that served to erect the modern biomedical public health policy system and marginalize or separate environmental approaches and institutions since the early twentieth century. Through a close reading of legislative debates, and an examination of government expenditure patterns, the evolving intent and path of the nation's de facto public health policy are traced and examined. This analysis reveals that public health policy advocates worked to promote and institutionalize particular conceptions of what public health policy was and should be. The biomedicalization of public health policy and institutions, and the marginalization of environmental protection from public health institutions, were aspects of the same historical process. Policy makers and the public health community legitimated public health policy priorities through the rhetorical construction of a narrative of public health progress that simultaneously elevated the promises of biomedicine and deemphasized the place of environmental sanitation or protection. These conceptions were institutionalized through legislation, administrative organization, and expenditure priorities. The institutionalization of biomedical agendas and conceptions came at a cost to earlier environmental identities and prerogatives. The reemergence of an environmental crisis in the late 1950s brought forth new policy opportunities and, more importantly, new policy claimants over the domain of environmental sanitation or pollution control. When the new policy actors vied for control of pollution management, they encountered and capitalized on the atrophied relationship between public health institutions and the environment. Creation of the Environmental Protection Agency in 1970 marked the birth of a new policy domain and the further fragmentation and marginalization of environmental approaches for public health institutions and policy. Nevertheless, public health remains a central and pressing concern for environmental institutions and policy, and conversely, environmental management remains an important part of public health policy.