There have been a number of changes in monetary policy rules in the United States and UK since the early 1960s. The Lucas critique says that this should induce changes in the equilibrium law of motion. This article summarizes reduced-form evidence on the evolving law of motion for inflation in the USA and the UK. Since the 1970s, inflation has become lower on average, less volatile and less persistent. There is also less uncertainty about the central bank's long-run target for inflation.