This article accounts for the boom in homeownership from 1994 to 2005 by examining the roles of demographic changes and mortgage innovations. To measure the impact of these factors, we construct a quantitative general equilibrium overlapping generation model with housing. In the long-run, mortgage innovation accounts for between 56 and 70% of the increase whereas demographics account for a much smaller portion. We test this result by considering changes in mortgages after 1940. We find that the introduction of the conventional fixed rate mortgage accounts for at least 50% of the observed increase in homeownership during that period. Copyright � (2009) by the Economics Department of the University of Pennsylvania and the Osaka University Institute of Social and Economic Research Association.

Mortgage loans are a striking example of a persistent nominal rigidity. As a result, under incomplete markets, monetary policy affects decisions through the cost of new mortgage borrowing and the value of payments on outstanding debt. Observed debt levels and payment to income ratios suggest the role of such loans in monetary transmission may be important.A general equilibrium model is developed to address this question. The transmission is found to be stronger under adjustable-than fixed-rate contracts. The source of impulse also matters: persistent inflation shocks have larger effects than cyclical fluctuations in inflation and nominal interest rates. JEL Classification Codes: E32, E52, G21, R21.

______________________________________________________________________The quantitative macroeconomics literature has documented that in the basic Overlapping Generations model a privatization of the social security system, going from a Pay-As-You-Go to a Fully Funded system, generates large long run welfare gains at the cost of substantial welfare losses for initial generations. We propose an alternative to previous literature. In this paper we maximize over the entire policy space, following the optimal fiscal policy approach, rather than comparing alternative policy paths one to one. That is, policies are chosen as part of the optimal design of a social security privatization in a Pareto improving way. The government decides endogenously how to finance the implicit social security liabilities and compensate the initial generations alive during the transition. In contrast with previous analysis the resulting allocation, by construction, lies on the constrained Pareto frontier. We find that the optimal design of reforms exhibits sizeable welfare gains, arising because of the reduction in labor supply distortions. In contrast, the welfare gains coming from the reduction of savings distortions are relatively small.