This book aims to report on a cutting-edge research project of the smart grid in Japan, resting on the three pillars of field experiments, behavioral economics, and big data. The field experiments on the smart grid were conducted in four regions in Japan—Yokohama city, Toyota city, Keihanna Science City, and Kitakyushu city—over a three-year period from 2012 to 2014 after the Great East Japan Earthquake on March 11, 2011, and the subsequent accident at the Fukushima Nuclear Power Plants. Our focus here is on demand response in the smart grid environment, which we also discuss in the context of power system reforms. The book is intended for undergraduate and graduate students, researchers, policy makers, and business leaders.