The summit of the 30-member NATO was the first of its kind Biden attended as US President, after four years of chaos seen under his predecessor Donald Trump, who called the military alliance "obsolete."
NATO Secretary-General Jens Stoltenberg told reporters on Monday morning the leaders were meeting "at a pivotal moment for our alliance, and today we'll open a new chapter in our trans-Atlantic relationship."
Stoltenberg noted that the summit will address the "NATO 2030" agenda, a comprehensive initiative about making sure the alliance remains ready today to face tomorrow's challenges.
He said that the leaders at the summit will strengthen Article V of NATO's founding treaty, which stipulates that an attack on one will be considered an attack on all, adding that NATO's operation area will cover not only air, sea and land, but also cyberspace and space.
Among the concerns NATO is facing is how to reconcile its role with the increasing defense autonomy the European Union (EU) wants. French President Emmanuel Macron has emphasized the importance of Europe in the Western defense alliance, tweeting that it was Europe's destiny to play a balancing role in the world in the future.
The summit will also touch on the bloc's relations with Russia and China, and the aftermath of its military withdrawal from Afghanistan.
