This book is dedicated to the proposition that health policy should be evidence-based, and that epidemiology can provide much of the evidence. Unlike most textbooks of epidemiology, which focus on etiologic research, it emphasizes the descriptive methods that are more relevant to policy. Part I introduces the subject of policy and its formulation, reviews selected methods that are generally relevant to health policy, and provides an overview of health data and their manipulation. Part II proceeds through the policy cycle: assessing population health status, assessing potential interventions, making policy choices; implementing and finally evaluating policy. At each step it identifies the potential contributions of epidemiology and describes and demonstrates relevant methods. Many practical examples are provided, drawn from several developed countries, but mathematics is kept to an elementary level. A recurring theme is the interaction between health phenomena and the underlying population dynamics, and thus the close relationship of this type of epidemiology to demography.