The article discusses how joining an exchange-rate union, like the European Monetary System, can impact member countries differently. By using a three-country model, the study shows that the union can stabilize exchange rates but may increase price variability in one country. The effects depend on the source of economic disturbances, trade between members, financial market integration, and price responsiveness. The union fixes exchange rates between member currencies, but this can lead to price fluctuations in one country. The level of financial integration and domestic price adjustments also play a crucial role in determining the benefits or drawbacks of joining the union.