Rising food and oil costs, an uncertain global economy, climate change and Zimbabwe's political crisis face the G8 leaders who are gathering in Japan.
The summit is being held at a secluded resort on the northern island of Hokkaido guarded by some 20,000 police.
Protesters have been gathering ahead of the three-day forum starting on Monday.
A US official said the gathering was likely to "strongly condemn" Zimbabwe's President Robert Mugabe over a disputed presidential election run-off vote.
The Group of Eight (G8) consists of Britain, Canada, France, Germany, Italy, Japan, Russia and the United States.

Leaders begin arriving on Sunday. US President George W Bush arrived in time to celebrate his 62nd birthday in Japan.
China, India and South Africa will be among other key nations attending.
Japan has spent a record sum of money and deployed about 20,000 police to seal off the summit at the remote lakeside resort of Toyako.
Several thousand demonstrators marched through Sapporo, the city closest to the venue, on Saturday, demanding that G8 leaders take action on global warming, poverty and rising food prices.
Four people were arrested in minor scuffles with police.
Violent anti-globalisation marches have marred past G8 meetings.

Food reserve system
Last year, Japanese officials said this summit would be about climate change and reaching agreement on a post-Kyoto Accord framework to cut greenhouse gas emissions, says the BBC's Chris Hogg in Tokyo.
Japanese Prime Minister Yasuo Fukuda had said he would like to get agreement on 50% overall reductions in greenhouse gases by 2050.
But the rising food and oil prices and their effect on the global economy and the world's poorest nations have moved up the agenda and to address them, China, India and several African nations have been invited to attend.
Japanese newspaper Asahi Shimbun reported that the G8 countries wanted to create a system of food reserves that would act to stabilise prices.
There has been a number of food riots in a range of countries over prices that the World Bank says have doubled in the past three years.
Another key issue will be North Korea's nuclear programme.
Mr Bush will meet Mr Fukuda amid Japanese concern that the North's recent declaration of its nuclear activities has led the US to signal removing Pyongyang from a terror blacklist.

Zimbabwe violence
South African President Thabo Mbeki will attend, fresh from crisis discussions in Zimbabwe on Saturday with President Robert Mugabe about last month's disputed election.
He has been the chief regional negotiator on the Zimbabwe crisis, and has been trying to persuade Mr Mugabe to form a government of national unity.
The main opposition party, the Movement for Democratic Change, pulled out of last month's second round presidential election vote, citing campaign violence.
On the way to Japan, a White House official said that the G8 would "strongly condemn what Mugabe has done".
A small group of African states has joined the European Union, the US and other Western nations in criticising the way the election was run.

Rising costs to dominate G8 talks

Rising food and fuel prices are set to top the agenda for leaders of the world's major industrialised nations as they start a key summit in Japan.
At the opening lunch of the Group of Eight (G8) nations, African leaders will set out the effect price rises are having on the world's poorest people.
The UK's Prime Minister Gordon Brown is expected to call for a doubling of food production in Africa.
Leaders are also seen tackling issues such as Zimbabwe, and aid to Africa.

Food focus
The G8 summit has opened at a resort on the northern island of Hokkaido.
Leaders from member nations - Britain, Canada, France, Germany, Italy, Japan, Russia and the United States - will be joined by counterparts from some 15 other countries, including eight African states.
Japan has spent a record sum of money and deployed about 20,000 police to seal off the remote lakeside town of Toyako for the three-day talks.

The impact on the global economy of price rises and other shocks such as the credit crunch have eclipsed other concerns, correspondents say.
The BBC's political editor, Nick Robinson, who is travelling to the summit with the UK prime minister, says Gordon Brown will join other leaders in calling for the doubling of food production in Africa.
Our correspondent says the G8 may call for the creation of a panel of international experts to advise on how to predict and hopefully avoid another crisis like this.
The EU has already been spelling out plans to alleviate the food crisis.
European Commission President Jose Manuel Barroso told reporters on the sidelines of the summit the proposed 1bn euro ($1.6bn, £800m) fund to help poor farmers in developing countries would come from unused EU subsidies.

It could help improve farmers' access to seeds and fertilisers, and could provide "safety net measures for the most vulnerable", he said.
The G8 leaders may also face tough questions on aid commitments to Africa. Three years ago they promised to double aid to the continent by 2010 - but campaigners say they are falling far short of that target.
As well as discussing development issues in Africa, the G8 leaders are widely expected to condemn Robert Mugabe's controversial re-election in Zimbabwe last month.
As he headed to the summit, UN chief Ban Ki-moon said he would discuss the crisis with African leaders there.
Zimbabwe's political parties should "work out an arrangement so that they can really bring back democratic rules, the rule of law and peace and stability in their country", he told the French news agency AFP.

Malaysia summit
A number of other bilateral meetings are taking place on the sidelines of the summit.
Mr Bush, attending his last G8 summit, and Russian President Dmitry Medvedev, attending his first, made little progress on the issue of the US plan for missile defence installations in the Czech Republic and Poland.

The two leaders instead cited areas where they had found common ground: preventing Iran from obtaining nuclear weapons and ending North Korea's nuclear weapons programme.
Mr Brown will also have talks with Mr Medvedev.
Meanwhile, the charity Water Aid has told the G8 that the single most effective measure it could take to prevent the deaths of millions of children in poor countries would be to build toilets and provide clean water.
Hundreds of protesters again marched through Sapporo on Sunday, the city closest to the venue, on the eve of the talks to demand G8 leaders take action on global warming, poverty and rising food prices.
The demonstration, which followed a similar protest on Saturday, was heavily policed and ended peacefully.
Violent anti-globalisation marches have marred past G8 meetings.
As the G8 got under way in Japan, leaders of the world's largest Islamic nations assembled for what is being billed as the D8 summit in Malaysia's capital, Kuala Lumpur, with the issue of inflation high on the agenda there.

G8 hails broad accord on climate

Leaders from the world's developed nations have agreed a "shared vision" on climate change with rising economic powers at the G8 summit in Japan.
But no specific agreements have been announced, and India and China have reportedly dismissed the rich nations' target of halving emissions by 2050.
Leaders from eight emerging economies held talks with the Group of Eight rich nations on the final day of the summit.
A US official said the broad agreement represented progress.
Jim Connaughton, chairman of President Bush's Council of Environmental Quality, told the Associated Press that the agreement "will give us greater confidence and commitments as we go to next year".
A statement on behalf of all 16 nations said they recognised the need for "deep cuts" in global greenhouse gas emissions to fight global warming.
But it stopped short of urging numerical targets for those reductions.

Global problems
On Tuesday the G8 group - which includes the UK, US, Canada, France, Germany, Italy, Japan and Russia - agreed to halve harmful emissions by 2050.
But emerging countries and environmentalists were scathing of the announcement.
And China's President Hu Jintao used his speech at the summit to urge all countries - particularly developed countries - to slash farm subsidies and trade barriers to calm soaring food prices.
Mr Hu was at the meeting as part of an "outreach" group of the world's fastest-growing economic powers.
China along with Brazil, Mexico, India and South Africa negotiated with the G8 countries for most of the morning.
They were joined by the leaders of Indonesia, South Korea and Australia for the discussion on climate change.
The BBC's diplomatic correspondent, Bridget Kendall, said the inclusion of eight emerging nations is an admission that G8 decisions on their own are no longer enough - global problems need global solutions.

Varied discussions
On the sidelines, Indian Prime Minister Manmohan Singh and US President George W Bush discussed a nuclear deal which has been stalled for the past three years.
The US agreed to help India with its civil nuclear programme more than three years ago, but Mr Singh has faced fierce opposition from left-wing parties in his governing coalition.
No announcement was made on the nuclear deal but Mr Singh said he was "very pleased" with US relations.
The summit, in Toyako, northern Japan, has seen G8 leaders voicing concern about soaring oil and food prices, the situation in Zimbabwe, and the pace of aid being sent to Africa.
But climate change has been one of the stickiest issues - with the G8's position receiving a volley of criticism from both environmentalists and developing nations.

World leaders avoid setting greenhouse target

TOYAKO, Japan (CNN) -- Leaders of the world's major economies pledged to combat climate change Wednesday -- but they did not set specific targets for reductions in greenhouse-gas emissions.

The economic powers -- including several developing nations -- did not go as far in their climate change statement Wednesday as the G-8 did the day before.

The G-8 endorsed the idea Tuesday of halving greenhouse gas emissions worldwide by 2050. The larger group of economic powers that weighed in Wednesday did not mention targets for reduced emissions.

"Conscious of our leadership role in meeting such challenges, we, the leaders of the world's major economies ... commit to combat climate change in accordance with our common but differentiated responsibilities and respective capabilities," the leaders said in a statement.

The statement came from economic powers that make up the G-8 -- Canada, France, Germany, Great Britain, Italy, Japan, Russia and the United States -- as well as Australia, Brazil, China, the European Union, India, Indonesia, South Korea, Mexico and South Africa.

The major economic powers met on the sidelines of the three-day G-8 summit in Japan and say they are proposing a balanced approach to dealing with climate change.

"We support a shared vision for long-term cooperative action, including a long-term global goal for emission reductions, that assures growth, prosperity, and other aspects of sustainable development," their statement said.

"Taking into account assessments of science, technology, and economics, we recognize the essential importance of enhanced greenhouse gas mitigation that is ambitious, realistic, and achievable." iReport.com: What green steps are you taking?

The leaders said they were uniting under the U.N. Framework Convention on Climate Change.

Ten years ago, the convention passed the Kyoto Protocol with the goal of limiting greenhouse gas concentrations in the atmosphere. The U.S. was the only one of 175 parties to reject it.

Washington has long argued that emerging economic powers China and India should be required to address their rapidly rising emissions.

U.S. President George W. Bush opposed the Kyoto Protocol because it did not include strict emissions limits for China and India. He said Wednesday's meeting represented a big move forward in addressing global warming.

"We made progress -- significant progress -- toward a comprehensive approach," Bush said. "In order to address climate change, all major economies must be at the table, and that's what we had here today."

During the Bali conference on climate change last year, the U.S. reluctantly signed an agreement calling for two years of additional negotiations on reducing carbon dioxide emissions.

The Bali pact is meant as a guide for more climate talks, which will culminate in Copenhagen, Denmark, in 2009.

The EU is already on record wanting an agreement to require developed countries to cut their emissions by 25 to 40 percent of 1990 levels by 2020.

The U.S., Japan and Canada oppose those targets.