For the open economy, the workhorse model in intermediate textbooks still is the Mundell-Fleming model, which basically extends the investment and savings, liquidity preference and money supply (IS-LM) model to open economy problems. The authors present a simple New Keynesian model of the open economy that introduces open economy considerations into the closed economy consensus version and that still allows for a simple and comprehensible analytical and graphical treatment. Above all, their model provides an efficient tool kit for the discussion of the costs and benefits of fixed and flexible exchange rates, which also was at the core of the Mundell-Fleming model. (Contains 11 figures and 11 notes.)