标签：#iso3166

Any application that ships across borders needs a way to name a country. You reach for a two-letter code, write US , JP , DE , and move on. Then a support ticket arrives. A user in Belfast picked "United Kingdom" and your shipping API rejected UK . Someone in Pristina found no option at all. Your analytics dashboard shows a country called AN that dissolved in 2010. These bugs share one root: ISO 3166-1 alpha-2 carries more rules than its two characters suggest. Let's walk through the parts that break real applications, and how to model country data so the next revision of the standard does not break yours. Key takeaways ISO 3166-1 defines 249 officially assigned alpha-2 codes. UK is not one of them. The United Kingdom is GB . Four other status categories exist: user-assigned, exceptionally reserved, transitionally reserved, and indeterminately reserved. They follow different rules. Kosovo uses XK , a code from the user-assigned range that ISO has never officially assigned. Codes get recycled. CS meant Czechoslovakia, then Serbia and Montenegro. Country names change far more often than their codes. Store the code, resolve the name at render time. What alpha-2 covers ISO 3166 splits into three parts. Part 1 names countries and their dependent territories. Part 2 names subdivisions inside them. Part 3 records codes that fell out of use. Part 1 gives you three code sets for the same entity: Format Japan Notes Alpha-2 JP Two letters. Used by ccTLDs, BCP 47 language tags, payment APIs. Alpha-3 JPN Three letters. Easier to read on its own. Numeric-3 392 Digits from UN M49. Script-independent, survives alphabet changes. Alpha-2 is the set you meet most often. Two characters fit anywhere, and the Internet Assigned Numbers Authority (IANA) draws the country-code top-level domains straight from the alpha-2 list, which puts these codes in front of everyone who ever registered a domain. That reach explains the misuse. Five kinds of code The 249 official codes get the attention.