Why should Europe opt for monetary union? “One Market needs one Money!”: This is, at first sight, the key argument of the influential report of the European Commission entitled “One Market, One Money”, published in 1990. Closer examination reveals a somewhat different picture, however. The extended subtitle is rather more agnostic: “An evaluation of the potential benefits and costs of forming an economic and monetary union.” A closer inspection of the report reveals that the key argument was the other way round: one money would create one market. Unfortunately, the authors in 1990 did not recognise that “one money” would foster huge cross-border financial flows that would one day lead to a very costly financial crisis.