Book excerpt: Epidemiology Matters offers a new approach to understanding and identifying the causes of disease -- and with it, how to prevent disease and improve human health. Utilizing visual explanations and examples, this text provides an accessible, step-by-step introduction to the fundamentals of epidemiologic study, from design to analysis. Across fourteen chapters, Epidemiology Matters teaches the individual competencies that underlie the conduct of an epidemiologic study: identifying populations; measuring exposures and health indicators; taking a sample; estimating associations between exposures and health indicators; assessing evidence for causes working together; assessing internal and external validity of results. With its consequentialist approach -- designing epidemiologic studies that aim to inform our understanding, and therefore improve public health -- Epidemiology Matters is an introductory text for the next generation of students in medicine and public health.