This is the CodeSystem that contains all the codes in ISO 3166 Part 1 Country Codes, 2nd Edition, Alpha-3 (http://terminology.hl7.org/CodeSystem/iso3166-1edition2alpha3) and ISO 3166 Part 1 Country Codes, 2nd Edition, Alpha-3 (http://terminology.hl7.org/CodeSystem/iso3166-1edition2alpha3). E.g. what you have to deal with if you get resources containing codes in either of them