Leaders from the world's richest countries are due to attend the annual G7 summit in the Bavarian Alps in Germany.
They are expected to use the meeting to maintain diplomatic pressure on Russia over the conflict in eastern Ukraine.
Greece's debt crisis and how to tackle global warming will also be on the agenda.
Russia has been excluded from what was previously known as the G8, since the annexation of Crimea last year.
President Vladimir Putin will be a major focus of attention, due to concerns that he is deliberately building up further military pressure in eastern Ukraine.
Nothing to fear
Germany, Britain and the United States want to reach an agreement to offer support to any EU member state tempted to withdraw backing for the sanctions on Moscow, which are hurting the Russian economy.
The West has been increasing its military presence in eastern European countries in response to concerns about Russian interference.
But Mr Putin said on Saturday that Russia was not a threat and had "other things to worry about".
He told the Italian newspaper Corriere della Sera: "Only an insane person and only in a dream can imagine that Russia would suddenly attack Nato.
"The world has changed so drastically that people with some common sense cannot even imagine such a large-scale military conflict today."
Ahead of the G7 gathering, thousands of protesters marched in the nearby town of Garmisch-Partenkirchen, sparking sporadic clashes with police.
Several marchers were taken to hospital with injuries, but the violence was minor compared to some previous summits.
US President Barack Obama, Japanese Prime Minister Shinzo Abe, UK PM David Cameron French President Francois Hollande, Canada's PM Stephen Harper and Italian PM Matteo Renzi will be greeted by German Chancellor Angela Merkel in Bavaria, under the presence of 17,000 police officers.
Mrs Merkel will also be hoping to use the summit to discuss her plans for radical reform of global responses to pandemics like Ebola.
She wants to streamline and re-focus the World Health Organization, widely judged to have been ill-equipped when Ebola hit, and build up an international reserve force of doctors and scientists for deployment in a future crisis.
On Monday, the summit is also due to discuss militant threats from groups like Islamic State and Boko Haram with the leaders of Nigeria, Tunisia and Iraq, who form part of an "outreach" group of non-G7 countries.