This text introduces medical and healthcare students to the basic principles and methods of epidemiology, with an emphasis on practical applications in both public health and clinical practice. Topics include the causes of cancer; effective methods of prevention of disease; targeting of high-risk populations; evaluation of new drugs and other therapeutic and preventive modalities; disease screening and early detection; and alternative methods of delivering health care. The text in organized into three sections: The Epidemiologic Approach to Disease and Intervention, Using Epidemiology to Identify the Causes of Disease, and Applying Epidemiology to Evaluation and Policy.