Up to and including the seventh edition of STANAG 1059, these were two-letter codes (digrams).
Additional codes cover gaps in the ISO coverage, deal with imaginary countries used for exercise purposes, and designate large geographical groupings and water bodies (ranging from oceans to rivers).
The ninth edition's ratification draft was published on 6 July 2005, with a reply deadline of 6 October 2005.
It is intended as a transitional standard: once all NATO nations have updated their information systems, a tenth edition will be published.
For diplomatic reasons, the country that is now known as North Macedonia was designated as the Former Yugoslav Republic of Macedonia for a number of years and received a temporary code, FY/FYR, explicitly different from the ISO one, which was 3166 MKD.