ISO 3166-1 defines codes for the names of countries, dependent territories, and special areas of geographical interest. The official name of the standard is Codes for the representation of names of countries and their subdivisions – Part 1: Country codes.
There are 3 sets of codes defined:
- Two-letter (alpha-2): the most commonly used set which assigns 2 letters to represent each country (e.g. HT for Haiti). These are also the basis for the domain country codes, although there are some variations.
- Three-letter (alpha-3): these are not as widely used as alpha-2 but the longer code does make it easier to recognise which country the code applies to (e.g. HTI for Haiti).
- Three-digit (numeric): not as easily understood by a reader but useful for situations where non-Latin script is used and therefore is less dependant on any specific language (e.g. 332 for Haiti).