Article 4 lets any NATO ally call the others to formal consultations when it feels its territory, independence or security is threatened. It commits nobody to fight.
It has been invoked nine times since 1949, most recently by Poland and Estonia in September 2025.
The text
Article 4 of the North Atlantic Treaty is one sentence: “The Parties will consult together whenever, in the opinion of any of them, the territorial integrity, political independence or security of any of the Parties is threatened.”
“In the opinion of any of them” means a single ally decides when it feels threatened; nobody can veto the request to talk. And “consult” means a meeting and a hearing.
What happens next
The request goes to the North Atlantic Council, NATO’s principal political body, where all 32 allies are represented. The Council discusses the threat and can agree on joint action. Like every NATO decision, that action needs consensus: there is no voting, and anything one ally objects to does not happen. So Article 4 cannot force a response, but it puts the threat on the table of all 32 governments at once.
The most recent example shows how it works. On the night of 9 to 10 September 2025, Poland counted 19 violations of its airspace by Russian drones, and three or four were shot down, by Tusk’s count. Poland invoked Article 4 the same day. On 12 September NATO announced Eastern Sentry, an operation to reinforce air defense along the eastern flank. Estonia followed with its own request after three Russian fighter jets entered its airspace on 19 September, and the Council met on 23 September.
The nine invocations
NATO lists every use:
- Türkiye, 10 February 2003, as war loomed in neighboring Iraq.
- Türkiye, 22 June 2012, after Syria shot down a Turkish military jet.
- Türkiye, 3 October 2012, after Syrian shells killed five Turkish civilians.
- Poland, 3 March 2014, over Russia’s actions in Ukraine.
- Türkiye, 26 July 2015, after terrorist attacks.
- Türkiye, 28 February 2020, after Turkish soldiers were killed in Idlib, Syria.
- Bulgaria, Czechia, Estonia, Latvia, Lithuania, Poland, Romania and Slovakia, 24 February 2022, the day Russia launched its full-scale invasion of Ukraine. It is one of the nine on NATO’s list.
- Poland, 10 September 2025, after the drone incursion.
- Estonia, 23 September 2025 (Council meeting), after the fighter jets.
The list says something about where the threats lie. Five of the nine came from Türkiye, on the alliance’s southern edge; every request since 2022 has come from the eastern flank.
Article 4 and Article 5
Article 4 is the step most crises stop at. Article 5 applies only to an armed attack, has been invoked once, in 2001, and commits each ally to help with “such action as it deems necessary.” Article 4 asks for less: a shared look at a threat and a chance to agree a response. It is also the usual route for hybrid incidents; see What is hybrid warfare?. The single Article 5 case is in Has Article 5 ever been invoked?
What it shows
Article 4 works because one ally can put a threat before all 32 governments within days. Nine requests since 1949, three of them since 2022, show how sharply the threat has moved to Europe’s east. They also show the limit: consultation produces action only as quickly as 32 governments can agree on it. Europe’s own contribution to what comes after the meeting is tracked in European defence in numbers.