Epidemiology is a population science that underpins health improvement and health care, and is concerned with the pattern, frequency, trends, and causes of disease. This book teaches its applications to population health research, policy-making, health service planning, health promotion, and clinical care. The book emphasizes concepts and principles. In 10 chapters, the book explains what epidemiology is; illustrates the basis of epidemiology in populations; provides a framework for analysing diseases by time, place, and person; introduces error, bias, and confounding; explains how we move from association to causation; considers the natural history, spectrum, and iceberg of disease in relation to medical screening; discusses the acquisition and analysis of data on incidence and prevalence of risk factors and diseases; shows the ways in which epidemiological data are presented, including relative and absolute risks; provides an integrated overview of study designs and the principles of data analysis; and considers the theoretical and ethical basis of epidemiology both in the past and the future. The emphasis is on interactive learning, with each chapter including learning objectives, theoretical and numerical exercises, questions and answers, and a summary. The text is illustrated, with detailed material in tables. The book is written in plain English, and the necessary technical and specialized terminology is explained and defined in a glossary. The book is for postgraduate courses in epidemiology, public health, and health policy. It is also suitable for clinicians, undergraduate students in medicine, nursing and other health disciplines, and researchers.