<Tr> <Td> Eurozone member states ERM II member states Other EU member states States using the euro as a result of a treaty States which have unilaterally adopted the euro </Td> </Tr> <P> There are 28 currencies currently used in the 50 countries of Europe, all of which are members of the United Nations, except Vatican City, which is an observer . All de facto present currencies in Europe, and an incomplete list of the preceding currency, are listed here . </P> <P> A currency is a medium of exchange, such as money, banknotes, and coins . In Europe, the most commonly used currency is the euro; any country entering the European Union (EU) is expected to join the eurozone when they meet the five convergence criteria . Denmark is the only EU member which has been granted an exemption from using the euro, Sweden has also not adopted the Euro, although unlike Denmark, it has not formally opted out, instead, fails to meet the ERM II (Exchange Rate Mechanism) which results in the non-use of the Euro . For countries which hope to join the eurozone, there are five guidelines that need to be followed, grouped in the Maastricht criteria . </P> <P> The pound sterling, used by the United Kingdom, is rated at fourth on Investopedia's list of the top 8 most tradable currencies, saying that it is a "little bit more volatile than the euro". It was ranked just ahead of the Swiss franc, ranked fifth, which is used in Switzerland and Liechtenstein, saying that the set up of the Swiss banking "emphasizes the economic and financial stability policies dictated by the governing board of the SNB". Both are in the top 8 major currencies on Bloomberg . Various countries use currencies which translate as "crown": the Czech koruna, the Norwegian krone, the Danish krone, the Icelandic króna, and the Swedish krona . </P>

What is the name of the currency used in the european union