-
ISO 3166-1 alpha-2 – two-letter country codes which are the most widely used of the three[citation needed], and used most prominently for the Internet's country code top-level domains (with a few exceptions).
-
ISO 3166-1 alpha-3: three-letter country codes which allow a better visual association between the codes and the country names than the alpha-2 codes.
-
ISO 3166-1 numeric – three-digit country codes which are identical to those developed and maintained by the United Nations Statistics Division, with the advantage of script (writing system) independence, and hence useful for people