While currency crises have been extensively studied, the opposite phenomenon, large appreciations, has been far less researched. We fill this gap by providing an empirical exploration of historical episodes of large real exchange rate appreciations, using a sample of 28 advanced and 25 emerging market economies, with annual data going back to 1970. We focus on the impact of large appreciations on output growth. Our first finding is that countries experiencing large real exchange rate appreciations display distinct patterns: large appreciations significantly lower export growth and boost import growth on impact. Strikingly, however, output growth is higher, on average, despite the adverse impact on exports. Our second finding is that these aggregate numbers hide substantial heterogeneity, which we link to the nature of the shocks that cause the appreciation. In particular, appreciations associated with so-called “capital flow bonanzas” have a marked downward effect on growth. This pattern is consistent with the insights from a simple model that contrasts the impact of productivity shocks with that of capital inflows shocks. Higher productivity in the traded sector leads to a boom in traded output and a current account surplus, while higher foreign lending leads to a boom in non-traded output and an external deficit as traded output falls and consumption increases.