Ranks and insignia of NATO

A NATO standard grade scale is used by the NATO and its partners for the purpose of comparing military ranks across the member nations militaries, as well as for a number of administrative tasks.
NATO maintains a "standard rank scale" which is also known as a "standardized reference system" in an attempt to standardize NATO codes of rank for military personnel and indicated correspondence with nations ranks. NATO's standardized reference system is intended to be used "by nations when preparing personnel tables, requisitions, reports and returns destined for NATO nations, organizations and commands."
The NATO rank reference code categories were established in 1978 in STANAG 2116 (formally titled NATO Codes for Grades of Military Personnel). The current- 7th - edition is just the cover, and the core of the standard is in set out in "NATO Codes For Grades Of Military Personnel" (APersP-01).
The NATO codes assigned for each grade are based on the agreed corresponding army grades with the naval and air forces grades determined from them by "national regulations".
OF-10 – OF-1 (highest to lowest rank code) are used for commissioned officers:
OR-9 – OR-1 (highest to lowest rank code) are used for other ranks (enlisted ranks and non-commissioned officers (NCO)):
For NATO purposes, NCOs are ranked OR-5 to OR-9. However, national rank structures might differentiate from this.
In the U.S. armed forces warrant officer is a separate and distinct category of officers. This officer rank and precedence is below those of officer personnel, but above that of non-officer personnel, and has a special group of codes (W-1 – W-5). In the Commonwealth tradition (for NATO the British Armed Forces and Canadian Armed Forces) warrant officers are the highest other ranks.
In the British Armed Forces senior non-commissioned officers are in OR-5 to OR-7 and junior non-commissioned officers (eg corporals) are in OR-3 and OR-4. In the U.S. military OR-5 and above are non-commissioned officers for the U.S. Army and U.S. Air Force but in the U.S. Marine Corps and U.S. Navy (both parts of the Department of the Navy), OR-4 and above are non-commissioned officers.
The numbers in the system broadly correspond to the U.S. uniformed services pay grades, with OR-x replacing E-x. The main difference is in the commissioned officer ranks, where the US system recognizes two grades at OF-1 level (O-1 and O-2), meaning that all O-x numbers after O-1 are one point higher on the US scale than they are on the NATO scale (e.g. a major is OF-3 on the NATO scale and O-4 on the US scale).
Appendix B of the APP-06 (related to STANAG 2019) standard lists 11 formation/unit groups (13 in US Armed Forces) and identifies the command level of seven of them:
This is a general NATO practice, which does not prevent individual branches of the armed forces, for example, the British Army, the U.S. Army and the U.S. Marine Corps, from having their own approaches to the positions held by certain officers and NCOs.
In 2010, Allied Command Operations and Allied Command Transformation produced NATO NCO Bi-SC Strategy and Recommended NCO Guidelines. The current Bi-SC joint document (19 December 2023) Directive 040-002 "NATO Non-Commissioned Officer and Junior Officer Bi-Strategic Command Employment and Development Strategy", describes the NATO rank indicators for NCOs:
Specific roles:
Based on the intentions of Bosnia and Herzegovina and Ukraine to join NATO, NATO codes for military ranks have been officially introduced in these countries. Bosnia and Herzegovina adopted a corresponding law in 2005. In Ukraine, the introduction of NATO codes for military ranks took place in two stages. Firstly in 2020, the Verkhovna Rada (Ukrainian parliament) amended the structure of military ranks which was followed in January 2021, by the Minister of Defense of Ukraine approving the compliance of military ranks with NATO codes by order though the order had a confidential status.
Some European NATO partners such as Austria and Ireland describe their ranks in terms of NATO rank codes for comparison with NATO forces. Finland also had a conversion table to NATO standards prior to becoming a NATO member.
General officer grades are usually defined by the number of stars they ‘wear’. In the first version of the STANAG, OF-6 to OF-10 were described as "to be used for one to five star ranks or equivalents respectively".