This paper considers the effect of currency union on exchange rate volatility. At a theoretical level, a simple framework is developed for thinking about volatility and exchange rate arrangements and some inferences are drawn from it. Empirically, the interaction between currency areas and exchange rate volatility is analysed by constructing counterfactual exchange rate series for the scenarios of currency union with Australia or with the United States from 1985 to 2001. We cannot confidently conclude that New Zealand's quarter-to-quarter exchange rate volatility would have been lower in a currency union with the United States or Australia. By contrast, cyclical variability in the New Zealand exchange rate has been greater over the last sixteen years than it would have been in a currency union with either Australia or the United States.