Which two-letter standard underlies most country flag emoji sequences?

Most country flag emoji sequences are based on ISO 3166-1 alpha-2 codes. Unicode converts each code’s two ASCII letters into a pair of Regional Indicator Symbols, which platforms commonly render as a flag.

For example, the country code US becomes the sequence 🇺🇸, while JP becomes 🇯🇵. The letters are not displayed literally because the Regional Indicator characters are designed to signal a possible flag sequence when used in pairs. Unicode’s region data also includes territories and other regions, so “country flag” is a useful shorthand rather than a perfect legal description.

A common mix-up is ISO 8601, which standardizes dates and times, and ISO 4217, which assigns three-letter currency codes such as USD and EUR. ISO 639-1 assigns two-letter language codes such as EN and FR, but those codes do not normally determine flag emoji. The emoji standard uses region identifiers that are closely tied to the ISO country-code system, with platform support determining how a sequence is drawn.