Mailath, George J. and Larry Samuelson (2006), Repeated Games and Reputations: Long-Run Relationships, Oxford: Oxford University Press.

It's a favorite and guide book of game theroy, if you concern about principal-agent problems.

Amazon's Review

"Repeated Games and Reputations is a much-needed addition to the ranks of advanced game theory books. It has features that will appeal to both economic theorists and applied economists in various fields. In addition to being a useful reference book, it would make a great textbook for a second field course in game theory and would be a useful supplementary reference in many microeconomic theory, macroeconomic theory and industrial organization field courses."--The Economic Record

"Repeated Games is comprehensive, self-contained, and extremely clear, with proofs that not infrequently improve on the originals. The book is an ideal text for part or all of a second graduate class in game theory, and will be a valuable aid for any student of the field."--Drew Fudenberg, Professor of Economics, Harvard University

"The theory of reputations in repeated games has become one of the most important areas of research in economic theory, because it offers essential insights into the foundations of economic and political institutions. The past decade has seen great progress in this area, especially in the study of games with imperfect private monitoring. George Mailath and Larry Samuelson have been active leaders in this research, and here they systematically lay out the state of the art. This book will be an important text and reference for years to come."--Roger Myerson, University of Chicago