I get a lot of queries about the difference between fixed and flexible exchange rates in terms of the options that each present a sovereign, currency-issuing government. I considered this question several times in the past. Many of those questions are pitched in terms of the basic macroeconomic framework for an open economy that appears in most mainstream macroeconomics textbooks, particularly those written in the 1970s, 1980s and 1990s. I am referring here to the Mundell-Fleming model which has been the mainstream staple for many years. The modern textbooks still teach these models but the exposition has evolved although remains deeply flawed. It seems that this conceptual framework is still used to make public comments along the lines that the US government is facing insolvency and that the euro remains the best monetary organisation for Europe. Those conclusions are as flawed as the model that spawns them. Flawed macroeconomic models lead to erroneous conclusions.