ISO 3166-2:FR is an ISO standard which defines geocodes: it is the subset of ISO 3166-2 which applies to France.
Each code consists of the ISO 3166-1 code FR and a hyphen followed by:
2 numbers for the metropolitan departments (except the two departements on Corsica which have 2A and 2B). The codes are identical with the standard departement numbering.
2 letters for the territorial collectivites and for the overseas territories, all of which have their own ISO 3166-2 entry.