This empirical study tries to identify the main determinants of housing starts by measuring the responsiveness of housing starts to the mortgage interest rate compared with economic fundamentals at the national and regional levels. If housing starts are not responsive to changes in the mortgage interest rate, then interventions by government-sponsored enterprises in the housing market that lower mortgage interest rates would not significantly affect housing starts. Econometric analysis of the supply side of the housing market suggests that economic fundamentals, not mortgage interest rates, drive housing starts. Therefore, shutting down Fannie Mae and Freddy Mac would likely have little effect on the housing starts.