The Beginnings of Behavioral Economics: Katona, Simon, and Leibenstein's X-Efficiency Theory explores the mid-20th century roots of behavioral economics, placing the origin of this now-dominant approach to economic theory many years before the groundbreaking 1979 work on prospect theory by Daniel Kahneman and Amos Tversky. It discusses the work of Harvey Leibenstein, Herbert Simon, George Katona, and Frederick Hayek, reintroducing their contributions as founding pillars of the behavioral approach. It concentrates on the work of Leibenstein, reviewing his nuanced introduction of X-efficiency theory. Building from these foundations, the work explores the body of empirical research on market power and firm behavior – XE relationship. This book is a tremendous resource for graduate students and early career researchers in behavioral economics, experimental economics, organizational economics, social and organizational psychology, labor market economics and public policy.