The paper considers the role of limits upon the permissible growth of public debt, like those e of fiscal instability, namely variations in the present value of current and future primary government budgets, necessarily results in price level instability, in the sense that there exists no possibile monetary policy that results in an equilibrium with stable prices. In the presence of sluggish price adjustment, the fiscal shocks disturb real output and real interest rates as well. On the other hand, shocks of this kind can be eliminated by a Maastricht-type limit on the value of the public debt. In the presence of the debt limit (and under assumptions of frictionless financial markets, etc.), “Ricardian equivalence” holds, and fiscal shocks have no effects upon real or nominal variables. Furthermore, an appropriate monetary policy rule can ensure price stability even in the face of other kinds of real shocks. Thus the debt limit serves as a precondition for the common central bank in a monetary union to be charged with responsibility for maintaining a stable value for the common currency.