Chapter 1 offers an introduction to the book. The book is an attempt to support the growing population health effort (a.k.a. “population health framework”), which offers solutions to public health’s well-documented problems. First the book outlines the field of population health science, along with how and why it has been making radical changes to public health theory and practice. Population health science is a discipline and reform movement that seeks to correct misguided theories and methods in mainstream twentieth century public health. But population health science is not well understood, or even known at all, outside of biomedical experts, and very little direct attention has been paid to it by professional philosophers. This book seeks to initiate a sustained dialogue about population health science. Next, this chapter gives an overview of the upcoming chapters, then proceeds to lay out the fields and literatures that the book will engage with, including: philosophy of science in practice, philosophy of medicine, public health ethics and health justice, and the history of population health science.