Currently, the International Organization for Standardization has introduced a three-letter system of codes (ISO 4217) to define currency (as opposed to simple names or currency signs), in order to remove the confusion that there are dozens of currencies called the dollar and many called the franc. Even the pound is used in nearly a dozen different countries, all, of course, with wildly differing values. In general, the three-letter code uses the ISO 3166-1 country code for the first two letters and the first letter of the name of the currency (D for dollar, for instance) as the third letter. United States currency, for instance is globally referred to as USD.
The International Monetary Fund uses a variant system when referring to national currencies.