Recent criticisms of the conduct and use of risk assessment by regulatory agencies have led to a wide range of proposed remedies, including changes in regulatory statutes and the development of new methods for assessing risk. The mandate to this Committee was more limited. Our objective was to examine whether alterations in institutional arrangements or procedures, particularly the organizational separation of risk assessment from regulatory decision-making and the use of uniform guidelines for inferring risk from available scientific information, can improve federal risk assessment activities. Before undertaking to determine whether organizational and procedural reforms could improve the performance and use of risk assessment in the federal government, the Committee examined the state of risk assessment and the regulatory environment in which it is performed. In this chapter, we define risk assessment and differentiate it from other elements in the regulatory process, analyze the types of judgments made in risk assessment, and examine its current government context. Because one chronic health hazard, cancer, was highlighted in the Committee's congressional mandate and has dominated public concern about public health risks in recent years, most of our report focuses on it. Furthermore, because activities in four agencies--the Environmental Protection Agency (EPA), the Food and Drug Administration (FDA), the Occupational Safety and Health Administration (OSHA), and the Consumer Product Safety Commission (CPSC)--have given rise to many of the proposals for changes in risk assessment practices, our review focuses on these four agencies. The conclusions of this report, although directed primarily at risk assessment of potential carcinogens as performed by these four agencies, may be applicable to other federal programs to reduce health risks.