We present evidence from the United States and the United Kingdom that the persistence of price inflation is significantly higher under managed-exchange-rate regimes than under gold-based, fixed-exchange-rate regimes. These differences are also reflected in expectations-augmented Phillips curves. We use a two-country macro model, with forward-looking price setters, to demonstrate that higher monetary accommodation of inflation and exchange-rate accommodation of inflation differentials increase inflation persistence. The evidence does not contradict this hypothesis. It supports the hypothesis of forward-looking price setters and highlights the empirical significance of the Lucas critique.