© The British Academy 2003. All rights reserved. This chapter examines the effects of monetary unification on market integration. It offers a new perspective on the Euro's likely effectiveness in achieving the 'Single Market' goal of European economic integration, by examining the impact of a nineteenth-century national currency reform. It looks back at the experience of Italian monetary unification after 1861 and describes how rapidly the prices of the basic factors of production, wages, and interest rates began to converge after the introduction of the national currency.