We analyze optimal monetary policy in a model with two distinct …nancial frictions.First, borrowing is subject to collateral constraints. Second, credit ‡ows are intermediated by monopolistically competitive banks, thus giving rise to endogenous lending spreads.We show that, up to a second order approximation, welfare maximization is equivalent to stabilization of four goals: in ‡ation, output gap, the consumption gap between constrained and unconstrained agents, and the distribution of the collateralizable asset between both groups. Following both productivity and …nancial shocks, the optimal monetary policy commitment implies a short-run trade-o¤ between stabilization goals. Such policy tradeo¤s become ampli…ed as banking competition increases, due to the fall in lending spreads and the resulting increase in …nancial leveraging.