Over the past decade, the concept of risk has become central to environmental policy. Environmental decision making has been recast as reducing risk by assessing and managing it. Risk assessment is increasingly employed in environmental policymaking to set standards and initiate regulatory consideration and, even in epidemiology, to predict the health effects of environmental exposures. As such, it standardizes the methods of evaluation used in dealing with environmental hazards. Nonetheless, risk assessment remains controversial among scientists, and the policy results of risk assessment are generally not accepted by the public. It is not my purpose to examine the origin of these controversies, which I and others have considered elsewhere (see, e.g., EPA 1987), but rather to consider some of the consequences of the recent formulation of risk assessment as specific decisions and authorities distinguishable from other parts of environmental decision making. The focus of this chapter is the relatively new policy of separating certain aspects of risk assessment from risk management, a category that includes most decision-making actions. Proponents of this structural divorce contend that risk assessment is value neutral, a field of objective scientific analysis, while risk management is the arena where these objective data are processed into appropriate social policy. This raises relatively new problems to complicate the already contentious arena of environmental policy. This separation has created problems that interfere with the recognition and resolution of both scientific and transscientific issues in environmental policymaking. Indeed, both science and policy could be better served by recognizing the scientific limits of risk-assessment methods and allowing scientific and policy judgment to interact to resolve unavoidable uncertainties in the decisionmaking process. This chapter will discuss the forces that encouraged separating the performance of assessment and management at the EPA in the 1980s, which I characterize as an uneasy divorce. I shall examine some scientific and policy issues, especially regarding uncertainty, that have been aggravated by this policy of deliberate separation. Various interpretations of uncertainty have become central, and value-laden issues in decision making and appeals to uncertainty have often been an excuse for inaction.