The euro, which is the currency of the European Union member states in the eurozone, has been used internationally since its launch in 1999. On 1 January 2002, when the currency formally replaced 12 currencies of the original eurozone states, its usage was inherited in territories such as Montenegro which had used pre-euro currencies, while other minor currencies tied to pre-euro currencies were also replaced by the euro, such as in Monaco. Four small states have been given a formal right to use the euro, and to mint their own coins, but all other usage outside the eurozone has been unofficial. With or without an agreement, these countries, unlike those in the eurozone, do not participate in the European Central Bank or the Eurogroup.
Its growing use in this regard has led to its becoming the only significant challenger to the U.S. dollar as the world's main reserve currency.
