I develop a version of the New Keynesian model with insider-outsider labor markets and hysteresis that can account for the high persistence of European unemployment. I study the implications of that environment for the design of monetary policy. The optimal policy calls for strong emphasis on unemployment stabilization which a standard interest rate rule fails to deliver, with the gap between the two increasing in the degree of hysteresis. A simple interest rule that includes the unemployment rate is shown to approximate well the optimal policy.