Barry Eichengreen via The Conversation |  New Year’s Day 1999 saw the largest monetary changeover in history. On that date, just 20 years ago, 12 members of the European Union formally adopted a brand-spanking-new currency, the euro. Today seven additional EU member states use it, along with Montenegro, Kosovo, Andorra, Monaco, San Marino and Vatican City. If survival is the ultimate gauge of success, then this grand monetary experiment can be said to have succeeded.