ISO 4217 is the international standard describing three letter codes (also known as the currency code) to define the names of currencies established by the International Organization for Standardization (ISO). The ISO 4217 code list is the established norm in banking and business all over the world for defining different currencies, and in many countries the codes for the more common currencies are so well known publicly, that exchange rates published in newspapers or posted in banks use only these to define the different currencies, instead of translated currency names or ambiguous currency symbols.

The first two letters of the code are the two letters of ISO 3166-1 alpha-2 country codes (which are similar to those used for national top-level domains on the Internet) and the third is usually the initial of the currency itself. So Japan's currency code becomes JPY—JP for Japan and Y for yen. This eliminates the problem caused by the names dollar, franc and pound being used in dozens of different countries, each having significantly differing values. Also, if a currency is revalued, the currency code's last letter is changed to distinguish it from the old currency. In some cases, the third letter is the initial for "new" in that country's language, to distinguish it from an older currency that was revalued; the code often long outlasts the usage of the term "new" itself. Examples of this include the Mexican peso (MXN) and the Turkish lira (TRY). Other changes can be seen, however; the Russian ruble, for example, changed from RUR to RUB, where the B comes from the third letter in the word "ruble".

There is also a three-digit code number assigned to each currency, in the same manner as there is also a three-digit code number assigned to each country as part of ISO 3166. This numeric code is usually the same as the ISO 3166 numeric code. For example, USD (US Dollar) has code 840 which is also the numeric code for US (United States).