Game theory has a very general scope, encompassing questions that are basic to all of the social sciences. It can offer insights into any economic, political, or social situation that involves individuals who have different goals or preferences. However, there is a fundamental unity and coherent methodology that underlies the large and growing literature on game theory and its applications. My goal in this book is to convey both the generality and the unity of game theory. I have tried to present some of the most important models, solution concepts, and results of game theory, as well as the methodological principles that have guided game theorists to develop these models and solutions. This book is written as a general introduction to game theory, intended for both classroom use and self-study. It is based on courses that I have taught at Northwestern University, the University of Chicago, and the University of Paris-Dauphine. I have included here, however, somewhat more cooperative game theory than I can actually cover in a first course. I have tried to set an appropriate balance between non-cooperative and cooperative game theory, recognizing the fundamental primacy of noncooperative game theory but also the essential and complementary role of the cooperative approach. The mathematical prerequisite for this book is some prior exposure to elementary calculus, linear algebra, and probability, at the basic undergraduate level. It is not as important to know the theorems that may be covered in such mathematics courses as it is to be familiar with the basic ideas and notation of sets, vectors, functions, and limits. Where more advanced mathematics is used, I have given a short, self-contained explanation of the mathematical ideas.