Abstract
A simple equilibrium model is presented which permits the joint study of optimal Central Bank prudential, monetary and balance sheet policies in the pre and post 2008 Crisis periods. It explains the new policies-the purchase of risky securities (QE), payment of interest on reserves (IR) and use of reverse repo (RRP)-as the response to the lack of safe assets in the economy, and shows why these policies were not needed to achieve optimality before 2008, but were needed for the 2008 Crisis and thereafter.