This is a rigorous, systematic introduction to the basic concepts and practical tools of epidemiologic research. It is aimed at readers who will be conducting epidemiologic studies themselves or who need a firm grasp of epidemiologic principles in order to interpret and evaluate studies conducted by others. Besides offering clear descriptions of key concepts, the book is rich with examples illustrating how these concepts are applied. Some examples are drawn from classic studies in the field--the work of Snow, Semmelweis, Goldberger, Doll and Hill, and others--while many others concern modern-day epidemiologic studies of problems of current public health importance. Almost every chapter includes a set of exercises (with answers) to help students gain practice in applying new ideas and techniques. The book's chapters are organized around three main themes: general concepts and methods of epidemiology; major study designs; and evaluating policies and programs. Collectively, these topics form the core material for a graduate-level course or course sequence in epidemiologic methods. Both authors are experienced epidemiologic researchers and have won multiple awards for effective teaching.