This paper offers a retrospective on the monetarist debate started by Milton Friedman in the 1950s, discussing both monetarist theory and policy recommendations. While the inability to find a controllable monetary aggregate with a velocity that can be accurately predicted has severely damaged the monetarist case, on other issues, such as the importance of changes in the monetary growth rate and the need to control inflation, the monetarist challenge to Keynesian orthodoxy was successful and made a central contribution to the currently prevailing macroeconomics.