Philosophy, Politics, and Economics (PPE) is a promising approach to understanding our complex world and addressing contemporary social issues. But what is it? This textbook aims to straightforwardly explain what PPE is to those who have never heard about it. The book uses a unified PPE approach which differs from a simple concatenation of moral philosophy, political science, and economics so that the reader can appreciate PPE's distinctiveness. It makes salient the virtues of PPE as a unified approach through a study of two liberal institutions that have been fundamental in making the world a better place: governments and markets. By the end, the reader will be confronted with the difficulty of finding only one right answer to unprecedented questions in a morally diverse society. Hopefully, however, readers will be convinced that the uncertainty of the diversity of our liberal societies is what has made them peaceful and prosperous despite the permanent frustration that results from living in a dynamic and complex world.