Montenegro became NATO’s newest member on Monday (5 June 2017), upon depositing its instrument of accession to the North Atlantic Treaty with the US State Department in Washington DC. At a ceremony marking the occasion, NATO Secretary General Jens Stoltenberg underlined that Montenegro’s accession to the Alliance contributes to international peace and security, and sends a strong signal that NATO’s door remains open. The ceremony was attended by Prime Minister Duško Marković and by the Minister of Foreign Affairs of Montenegro Srdjan Darmanović and was hosted by the United States Undersecretary for Political Affairs Thomas A. Shannon.

"Today, Montenegro joins NATO with a seat at the table as an equal, with an equal voice in shaping our Alliance, and its independence guaranteed," the Secretary General said. Mr. Stoltenberg noted that NATO will benefit from Montenegro’s insight into the Western Balkans "and the professionalism, bravery and dedication of its men and women in uniform". He stressed that NATO’s collective pledge, Article 5, has kept Allies safe for almost seven decades.

Allied Foreign Ministers signed Montenegro's Accession Protocol in May 2016, after which all 28 national parliaments voted to ratify Montenegro's membership. A flag-raising ceremony for Montenegro will take place at NATO Headquarters on 7 June 2017.

Today marks NATO's first enlargement since 1 April 2009, when Albania and Croatia joined the Alliance.