Overturning Mundell

"Central to ongoing debates over the desirability of monetary unions is a supposed trade-off, outlined by Mundell [1961]: a monetary union reduces transactions costs but renders stabilization policy less effective. If shocks across countries are sufficiently correlated, then, according to this argument, delegating monetary policy to a single central bank is not very costly and a monetary union is desirable"--Federal Reserve Bank of Minneapolis web site.