Thesis (Ph.D.)--Massachusetts Institute of Technology, Dept. of Economics, c1999.Includes bibliographical references.Chapter 1: I study the design and functioning of self-enforcing incentive contracts under imperfect observability, using a model of repeated agency that allows for both common and private performance monitoring. When performance measures are mutually observed, optimal relational agreements always keep the parties on the Pareto frontier. When performance measures are privately observed, self-enforcing agreements involve the possibility of separation on the equilibrium path, but optimal contracts still take a basic "termination" form. Using these results, one can view optimal long-term contracts as the solution to a static opti...