Stephen Cecchetti, Paul Tucker | Since the Global Crisis, the size of central bank balance sheets has grown significantly. Traditional goals of price and financial stability are insufficient for assessing the success of modern central banking operations. This column introduces a new framework for categorising and understanding central bank balance sheet operations. Monetary policy decisions are separated from facilities for lender of last resort, market maker of last resort, providing selective credit, and ensuring emergency government financing. To maintain legitimacy and accountability, central banks should formally distinguish these operations by clearly setting out their purposes, objectives, and constraints.