U.S. President Donald Trump and his 28 NATO counterparts are gathering in London on Tuesday to mark the 70th anniversary of the defence alliance.
However, their summit has been overshadowed by disputes about NATO’s purpose and strategic direction.
The two-day summit would trigger a reflection process aimed at strengthening political cooperation within NATO.
According to German government sources, this is broadly in line with a proposal by German Foreign Minister, Heiko Maas, to address problems within the alliance.
Recent events in north-eastern Syria prompted soul-searching, with French President Emmanuel Macron unleashing a storm of controversy by remarking on the brain death of NATO.
Others were quick to distance themselves from his comments.
In October, the U.S. pulled troops out of north-eastern Syria, without consulting NATO allies.
This paved the way for Turkey also a NATO member to attack Western-allied Kurdish militia, who had helped defeat Islamic State in the region.
However, the events will start with a breakfast meeting between Trump and NATO Secretary General, Jens Stoltenberg.
The U.S. president will also be holding talks with Macron later.
The 29 NATO leaders are to attend a reception with the queen at Buckingham Palace, followed by a visit to 10 Downing Street, the residence of British Prime Minister Boris Johnson.
Their formal talks will begin on Wednesday, when the leaders are due to hold a three-hour meeting in a golf resort north of London.
They have a list of around 50 decisions to formalise, adapting NATO to current and future threats.