In response to the Great Financial Crisis, the Federal Reserve and the Bank of England have adopted unconventional monetary policy instruments. We investigate if one of these, purchases of long-term government debt, could be a valuable addition to conventional short- term interest rate policy even if the main policy rate is not constrained by the zero lower bound. To do so we add a stylised financial sector and central bank asset purchases to an otherwise standard New Keynesian DSGE model. Asset quantities matter for interest rates through a preferred habitat channel. If conventional and unconventional monetary policy instruments are coordinated appropriately then the central bank is better able to stabilise both output and inflation. Keywords: Quantitative Easing, Large-Scale Asset Purchases, Preferred Habitat, Optimal Monetary Policy JEL-Classification: E40, E43, E52, E58