While it is a long-standing idea in international macroeconomic theory that flexible nominal exchange rates have the potential to facilitate adjustment in international relative prices, a monetary union necessarily forgoes this mechanism for facilitating macroeconomic adjustment among its regions. Twenty years of experience in the eurozone monetary union, including the eurozone crisis, have spurred new macroeconomic research on the costs of giving up nominal exchange rates as a tool of adjustment, and the possibility of alternative policies to promote macroeconomic adjustment. Empirical evidence paints a mixed picture regarding the usefulness of nominal exchange rate flexibility: In many historical settings, flexible nominal exchanges rates tend to create more relative price distortions than they have helped resolve; yet, in some contexts exchange rate devaluations can serve as a useful correction to severe relative price misalignments. Theoretical advances in studying open economy models either support the usefulness of exchange rate movements or find them irrelevant, depending on the specific characteristics of the model economy, including the particular specification of nominal rigidities, international openness in goods markets, and international financial integration. Yet in models that embody certain key aspects of the countries suffering the brunt of the eurozone crisis, such as over-borrowing and persistently high wages, it is found that nominal devaluation can be useful to prevent the type of excessive rise in unemployment observed. This theoretical research also raises alternative polices and mechanisms to substitute for nominal exchange rate adjustment. These policies include the standard fiscal tools of optimal currency area theory but also extend to a broader set of tools including import tariffs, export subsidies, and prudential taxes on capital flows. Certain combinations of these policies, labeled a “fiscal devaluation,” have been found in theory to replicate the effects of a currency devaluation in the context of a monetary union such as the eurozone. These theoretical developments are helpful for understanding the history of experiences in the eurozone, such as the eurozone crisis. They are also helpful for thinking about options for preventing such crises in the future.