Archive briefing · Event date: 4 April 2023. This retrospective summary was prepared on 4 November 2026.
Finland became NATO’s 31st member when its accession document was deposited with the United States at NATO headquarters in Brussels. The step completed the formal process of joining the alliance.
What happened
NATO’s members had signed Finland’s accession protocol in July 2022. The existing allies then approved membership through their national processes. A flag-raising ceremony in Brussels marked Finland’s arrival as a member.
Why it mattered
The decision changed Finland’s position from a close partner to a full member of the alliance. For readers looking back at Finland’s security-policy timeline, 4 April 2023 is the date to distinguish from the earlier application and ratification stages.
Source: NATO’s announcement, 4 April 2023. This is an archive summary, not a report of a new accession today.
