Chapter 1 reviewed the elements of risk assessment, a process in which predictive theories are used to estimate health effects at low doses because direct observations are not usually available. In the current system of chemical and radiation protection, risk information at small doses is necessary in regulatory decision making and in risk-management practices. Decision makers and regulators need a handle on risks to understand the public health impacts of dose limits and risk-management options. Risk-management practitioners use risk information to develop and implement cost-effective risk-reduction strategies.