This book was conceived as an intermediate epidemiology textbook. Similarly to the first and second editions. the third edition explores and discusses key epidemiologlc concepts and basic methods in n1ore depth than that found in basic textbooks ou epidemiology. For the third edition. ne,~1 examples and exercises have been added to all chapters. In Chapters 7 and 10. respectively, \Ve included discussions of novel epidemiologic strategies for handling confottnding (i.e .. instrumental variables and propensity scores) and of decision tree as a decision-making tool.