There are two kinds of currency code in the XRP Ledger:

* Three-character currency code. We recommend using all-uppercase [ISO 4217 Currency Codes](http://www.xe.com/iso4217.php). However, any combination of the following characters is permitted: all uppercase and lowercase letters, digits, as well as the symbols `?`, `!`, `@`, `#`, `$`, `%`, `^`, `&`, `*`, `<`, `>`, `(`, `)`, `{`, `}`, `[`, `]`, and <code>&#124;</code>. The currency code `XRP` (all-uppercase) is reserved for XRP and cannot be used by issued currencies.
* 160-bit hexadecimal values, such as `0158415500000000C1F76FF6ECB0BAC600000000`, according to the XRP Ledger's internal [Currency Format](currency-formats.html). This representation is uncommon.
