Andorra and the euro facto" used the EU's euro (the currency of the Eurozone states) as it had historically used the French franc and Spanish peseta. When those two currencies were replaced by the euro in 2002, the euro replaced the franc and peseta as the sole circulating currency in Andorra. Unlike the three other European microstates outside of the EU, Monaco, San Marino and the Vatican City, which adopted the euro when it was introduced, Andorra did not conclude a monetary agreement with the EU but rather used it unilaterally. These agreements gave the three microstates the right to issue their own euro
Optimum currency area rationale behind the creation of the euro is that the individual countries of Europe do not each form an optimal currency area, but that Europe as a whole does. The creation of the euro is often cited because it provides the most modern and largest-scale case study of an attempt to identify an optimum currency area, and provides a comparative before-and-after model by which to test the principles of the theory. In theory, an optimal currency area could also be smaller than a country. Some economists have argued that the United States, for example, has some regions that do not