ISO 3166-2:TO is the entry for Tonga in ISO 3166-2, part of the ISO 3166 standard published by the International Organization for Standardization (ISO), which defines codes for the names of the principal subdivisions (e.g., provinces or states) of all countries coded in ISO 3166-1.
Currently for Tonga, ISO 3166-2 codes are defined for 5 divisions. Each code consists of two parts, separated by a hyphen. The first part is TO, the ISO 3166-1 alpha-2 code of Tonga. The second part is two digits (01–05).