Intuitive as Mundell’s notion may be, we know of no formal study connecting mobility with macroeconomic adjustment within a currency union. To remedy this, we set up a currency union model featuring nominal rigidities and incorporate labor mobility across the different regions (or countries) that compose the currency union. We use this simple model to tackle two related questions. First, does mobility help stabilize macroeconomic conditions across regions in a union? Second, is equilibrium mobility socially optimal?