Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Economics, 2011.Cataloged from PDF version of thesis.Includes bibliographical references (p. 97-101).The first chapter examines the interaction of heterogeneous firms in a competitive market in which firms motivate their workers using relational incentive contracts. In the steady-state rational-expectations equilibrium, aggregate TFP is fully characterized by a weighted average of firm-specific sustainable effort levels. Relational contracts amplify exogenous productivity heterogeneity and lead to dispersion in the net marginal revenue product of labor. Improvements in formal contracting disproportionately benefits low-productivity firms, leading to a greater dispersion of the...