Boris Johnson and leaders of other Nato countries are meeting in the Spanish capital of Madrid on Tuesday for a two day summit billed as “pivotal” to the future of the West’s Transatlantic defence alliance.
The summit is taking place against the backdrop of Vladimir Putin’s brutal invasion of Ukraine - a conflict which has already cost thousands of lives and upended European security.
But the talks will also look beyond Russia to the security challenge presented by China as well as how to counter terrorism and threats posed by cyber and hybrid warfare.
Here the Evening Standard guides you through the summit, why it matters and the key decisions leaders are set to take.
What is Nato?
NATO - or the North Atlantic Treaty Organisation - is a military alliance made up of 30 member countries, including the US, founded in 1949 following the end of World War Two.
It exists to protect the people and territory of its members and is founded on the principle of collective defence, meaning that if one Nato ally is attacked, then all Nato Allies are attacked.
Following the end of the Cold War in the 1990s, there were questions over the purpose of the alliance but since Russia’s invasion of Crimea in 2014 defence spending by countries has increased and Vladimir Putin’s assault on Ukraine has led to a renewed sense of purpose and unity for the organisation.
What is the Nato summit?
Every year leaders of the 30 member countries come together to discuss the major threats faced by the alliance. This year the meeting, which starts on Tuesday afternoon and runs until Thursday lunchtime is being held at the IFEMA Conference Centre in Madrid.
Spain’s King Felipe VI will host a Royal Gala dinner on Tuesday night while world leaders will attend a reception and dinner at the Museo Del Prado on Wednesday evening.
Last year’s meeting in Brussels was the first to be held since Joe Biden replaced Donald Trump as US President and marked a major shift in the US’s attitude towards the alliance.
During the Trump administration, the US became sharply critical of Nato with the former President declaring the organisation “obsolete” and threatening to dramatically reduce defence spending in Europe.
By contrast President Biden has been keen for the US to play a bigger role on the world stage - an approach which has only hardened with Putin’s invasion of Ukraine.
Who’s attending?
Boris Johnson will join other G7 leaders including President Biden, French President Emmanuel Macron and Germany’s leader Olaf Scholz in flying to Madrid from the Bavarian Alps where they have been holding talks since the weekend.
As a NATO member, Turkey’s premier Recep Tayip Erdogan will also be present as well as the heads of so-called ‘partner’ countries including Australia’s newly elected Prime Minister Anthony Albanese.
Reporters will be watching closely to see what reception Mr Johnson gets from fellow Nato leaders during the traditional ‘family photo’.
At an extraordinary summit to discuss the Ukraine war in March, other leaders including Mr Macron appeared to snub the Prime Minister.
Unlike the G7 in Germany and the Commonwealth Heads of Government meeting in Rwanda last week, leaders’ wives including Carrie Johnson are not scheduled to be present.
What will countries do about Russia’s invasion of Ukraine?
As part of his appeal for more support to help his forces resist Putin’s invasion, Ukraine’s President Volodymr Zelensky will address the Nato summit by video link, probably on Wednesday morning.
President Zelensky is likely to ask for more heavy weaponry to help repel the Russian forces, who are now focusing their efforts on the eastern Donbas region of the country.
Nato members are expected to pledge further military and financial support for Ukraine.
Mr Johnson is also expected to continue to press Britain’s Nato allies to stiffen their resolve and prepare for a long conflict in Ukraine.
The challenge for Nato will be how to support Ukraine - which is not a member of the alliance - without triggering direct conflict with Russia.
How will Nato boost defences against Russian aggression?
As well as the immediate need to boost military support for Ukraine, Nato countries will also discuss plans to significantly bolster the alliance’s rapid response force in Europe from 40,000 troops to 300,000.
Nato Secretary General Jens Stoltenberg said on Monday the move was part of the "biggest overhaul of collective defence and deterrence since the Cold War."
Allies will be asked to strengthen their battlegroups on Nato’s eastern flanks, particularly in and around the Baltic countries Estonia, Lithuania and Latvia which fear being the next target for Putin’s aggression.
Mr Stoltenberg also said the alliance will work with Ukraine to modernise its defence systems over time, helping it shift its military hardware from the Soviet era to modern weapons technologies.
Will Finland and Sweden join?
One of the other major themes at the summit will be Sweden and Finland’s applications to join the alliance - which has risked further inflaming Western tensions with the Kremlin.
Turkey has blocked the applications so far, arguing the Scandinavian nations are soft on terror groups including the Kurdistan Workers Party or PKK.
Mr Erdogan has agreed to meet Finnish President Sauli Niinisto and the Swedish prime minister Magdalena Andersson on the sidelines of the summit and officials from the three countries have stepped up talks ahead of the Nato gathering in a bid to break the deadlock.
What about China?
While much of the summit will focus on the Russian threat, allies are scheduled to discuss Nato’s new strategic concept - an overarching vision for the future of the organisation.
This includes - for the first time - a joint position on China and how to handle Beijing’s security and strategic interests.
However it has been reported that allies are split on how tough the language on China should be with the US and UK said to be pushing for a much stronger stance to reflect Beijing’s more aggressive military ambitions and amid concerns it could attack Taiwan, sparking another global crisis.
But other countries with closer industrial ties to China would like to see a more measured approach.
How might the summit boost Boris Johnson’s ratings?
With the Prime Minister’s leadership under renewed scrutiny following last week’s disastrous by-election defeats in Wakefield and Tiverton and Honiton, Boris Johnson has been trying to shift attention to his role as an international statesman.
The Nato summit will give Mr Johnson another global platform to call for more support for Ukraine which his supporters say is far more important than the debate at Westminster about his future.
But ever since the by-election results came through early last Friday, his diplomatic tour has been dogged by questions over his leadership.
The Prime Minister may even have antagonised his opponents in the Tory party with claims that he was thinking actively about a third term in charge and that he wouldn’t underdog a psychological transformation following the defeats and the subsequent resignation of Conservative chairman Oliver Dowden.
