Across the last fifty years, epidemiology has developed into a vibrant scientific discipline that brings together the social and biological sciences, incorporating everything from statistics to the philosophy of science in its aim to study and track the distribution and determinants of health events. A now-classic text, the third edition of this essential introductory textbook gives an overview of the core concepts that form the underpinnings of epidemiology and epidemiologic research. Rather than focusing on statistics or formulas, Epidemiology presents the underlying epidemiologic principles and concepts in a coherent and straightforward exposition. This core content is supplemented with historical notes, a discussion of scientific inference, details about infectious disease epidemiology, and some advanced topics—including how to deal with missing data, the use of causal diagrams, and quantitative bias analysis techniques—that serve as an on-ramp into further study for those who elect to pursue it. By emphasizing a unifying set of ideas, students will develop a strong foundation for understanding the principles of epidemiologic research.