- Climate change
Image source, ReutersImage caption, The summit is being hosted by Italian Prime Minister Mario Draghi
Climate change and Covid are top of the agenda as leaders from the world's major economies meet in Italy.
It is the first time the G20 leaders are meeting face-to-face since the start of the pandemic.
However, China's Xi Jinping and Russia's Vladimir Putin will not be in Rome for the summit, choosing to appear via video link instead.
The meeting comes amid increasingly dire warnings for the future if urgent action is not taken to cut emissions.
The group – made up of 19 countries and the European Union – is estimated to account for 80% of the world's emissions.
Speaking ahead of the two-day summit, UK Prime Minister Boris Johnson suggested failing to act would result in "our civilisation" going backwards, consigning "future generations to a life that is far less agreeable than our own".
However, he acknowledged that neither the G20 meeting, nor the upcoming COP26 summit in Glasgow, which begins on Monday, would stop global warming, saying "the most we can hope to do is slow the increase".
According to Reuters news agency, a draft communiqué outlines a promise from the G20 to work towards limiting the rise in temperatures to 1.5C (2.7F) – but no legally binding agreement will be made.
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Mr Johnson is also expected to touch on coronavirus vaccine inequality during the summit, telling his fellow leaders "the pace of recovery will depend on how quickly we can overcome Covid", with the first priority being "the rapid, equitable and global distribution of vaccines".
More than six billion Covid vaccine doses have been administered worldwide. However, a letter addressed to Italian PM Mario Draghi, who is hosting the G20, from more than 160 former world leaders and global figures noted just 2% of people in low-income countries have received a jab.
Meanwhile, US President Joe Biden will push for countries to boost energy production, amid rocketing prices, as well as discussing a plan to prevent future pandemics.
The group is also expected to back a global minimum corporate tax rate of at least 15%, which is backed by 140 countries around the world.