ISO 4217 Currency Codes

The common pattern for a regular fiat currency code takes its first two letters from the country's ISO 3166-1 alpha-2 code and adds a third letter identifying the currency itself – GB + P for GBP, US + a designator for the dollar. Exceptions exist even within this pattern, such as USN ("US dollar, next day"), a settlement-timing variant of the US dollar rather than a distinct national currency.

A block of codes beginning with X followed by two further characters is reserved for currencies and quasi-currencies that do not name a single issuing country, and this bucket is itself a grab-bag of otherwise unrelated cases:

• Commodities used as currency, coded by periodic-table element – XAU for gold, XAG for silver.
• Currencies of territories rather than countries – XPF, the CFP franc ("franc Pacifique"), used across several French Pacific territories with no single national issuer.
• Operational and testing codes – XTS, reserved for software testing, and XXX, meaning "no currency" is applicable to the transaction at all.
• Supranational units – XDR, the IMF's Special Drawing Rights, a reserve asset rather than a circulating currency of any single jurisdiction.

A residual set of codes match neither the regular nor the X pattern. EUR is the clearest example: the Eurozone is not a country, so the "country code plus currency letter" rule that produces GBP or JPY has no country to start from, and the code exists as its own irreducible designator instead.

Beyond the alphabetic code, ISO 4217 assigns each currency a three-digit numeric code (978 for EUR, 840 for USD) and a count of minor unit digits – whether the currency divides into hundredths, thousandths, or some other fraction of its major unit. This field is the ISO ancestor of what a currency pair's own conventions later call decimal places or pip size (see the decimal_places field documented for currency pairs).

Being covered by ISO 4217 is a mark of formal recognition, not a precondition for behaving as a currency. Fiat currencies of smaller nations or territories not (yet) assigned an ISO code, the onshore/offshore pseudo-codes ORE Studio constructs for currencies with restricted circulation (documented in full for FX pairs, not repeated here), and cryptocurrency symbols all sit outside the standard while still functioning as currencies in every operational sense. Cryptocurrency symbols in particular are informal, community-driven conventions rather than a managed standard – BTC or XBT for Bitcoin, LTC for Litecoin, DOGE or XDG for Dogecoin – and unlike ISO codes they are not guaranteed unique or three-lettered; some clash directly with existing ISO 4217 codes, a reminder that a currency's code is only ever as authoritative as the community or standards body that maintains it (see Kinds of Money§"Cryptocurrency").