Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Economics, 2001.Includes bibliographical references.This thesis includes four essays on the macroeconomic effects of financial market imperfections. The first essay studies the incentives for banks that participate in an interbank market to keep a sufficient level of reserves. It presents a model where, in presence of imperfect insurance against bank-specific shocks, banks keep an inefficiently low ratio of reserves to deposits. A consequence of this is that the interest rate on the money market will fluctuate too much from a second-best perspective. It discusses the potential benefits and risks associated to central bank intervention, and highlights the complementarity betwee...