Across 14 developed-economy countries over the last half-century, we analyze the behavior of inflation once a country’s inflation rate surges past various thresholds and study how long a burst of inflation typically lingers. If history is a guide, inflation can take far longer to return to normal levels than most people realize. “Transitory” inflation is certainly possible, but it is hardly a sensible central expectation. Messaging and policy response from the US Federal Reserve Bank should reflect the relatively high empirical risk that inflation may persist.