Thousands of demonstrators have converged on Rostock in northern Germany, ahead of the G8 summit in nearby Heiligendamm. The BBC News website's Jacqueline Head examines the different groups protesting.
Who are the groups?
An estimated 30,000 people held protests at the weekend
There are a broad range of groups rallying, from environmental and anti-poverty campaigners to anti-globalisation and multi-faith groups, with one overarching common interest: social justice.
Organisations include the Global Call to Action against Poverty (GCAP), Greenpeace, Oxfam, Christian Aid, trade unions, Friends of the Earth, Block G8, Attac and "Black Bloc" demonstrators.
They are divided into two main thought camps.
One recognises the G8 as a legitimate way to bring about change, and uses the summit to lobby for causes they believe should be addressed or acted upon by the leaders.
The other is rallying against the notion of G8. They believe that having leaders from eight different nations making decisions on global issues is not democratic, and that those nations are responsible for many of the world's current problems.
What kind of people are marching?
There are a wide range of ages and nationalities attending rallies around the G8 summit.
Various ages and nationalities are represented in Rostock
They are reported to include boy scouts and over-50s groups.
Some movements, such as those under the Block G8 umbrella - a movement aiming to block the entrance to Heiligendamm - are made up primarily of young Germans, organisers say.
Others, such as GCAP or Greenpeace, have supporters in Germany from all over the world, including France, the UK, China, Japan, the Philippines and Africa, along with a wide range of ages.
What are the main issues for the protesters?
The most prominent issues centre on this year's G8 agenda - above all, poverty and climate change.
Many groups are calling for cancellation of developing nations' debt, trade justice, better healthcare, education, water and sanitation across the globe and action to tackle climate change.
Others are using the summit as a platform to draw attention to other issues, such as war and torture, GM crops, militarisation and "discriminatory" immigration policies.
GCAP are calling for the leaders to fulfil the promises they made at Gleneagles in 2005, saying that the G8 nations are falling short of the targets they originally set themselves.
Ciara O'Sullivan, GCAP spokesperson, said they plan to present UK Prime Minister Tony Blair and German Chancellor Angela Merkel with a petition of one million voices calling on them to fulfil their promises.
Tricia O'Rourke, spokesperson for Oxfam, said: "We are reminding them that they have to deliver."
"In 2005 in Gleneagles they promised they would increase aid to $50bn (£25bn) by 2010, but we recently calculated following current trends they will be short by $30bn."
Greenpeace have an action list they want the leaders to fulfil, which includes reducing carbon dioxide (CO2) emissions by 30% by 2020 and 80-90% by 2050.
The EU has pledged to slash CO2 emissions by 20% from 1990 levels by the year 2020, and UK ministers have outlined proposals to cut emissions by 60% by 2050.
Greenpeace campaigner Agnes de Rooij said there was no point in the G8 allocating aid to countries if they could not deliver on climate change.
"You can give aid to developing countries, but if you don't solve the climate problem it won't make any difference. They need to solve the climate problem or the aid won't be effective."
How are people protesting?
The majority of demonstrators are holding peaceful marches. Some have chosen to block roads with their bodies in an effort to stop traffic from entering Heiligendamm.
Others have drawn up action points they hope leaders will take note of, or petitions from different countries.
The majority are adamant that their protests are peaceful.
The Black Bloc, who include anarchists, wear black clothing and masks.
Campaigners on the ground say only a very small minority are involved in violence.
Why are people protesting against G8 itself?
Some people believe that the G8 is not a democratic method of making decisions that could affect the rest of the world, or that the countries involved are not effective in bringing about the right kind of change.
They want a more "democratic" approach - stemming from grassroots activism, rather than from the most powerful leaders in the world.
Block G8 is an umbrella of 125 groups organising a massive blockade against the summit.
Christoph Kleine, a spokesperson for the collective, said their protest is a "clear sign of our rejection of the G8 and our belief that the G8 is completely illegitimate.
"These are the governments of eight countries who think they can rule the world because they are the richest and most powerful. This is not democratic.
"We can see the result of domination by these countries - war, social injustice. They stand for the danger of climate change. They are the countries who are responsible for most of the emissions."
But other groups take a contrasting view and use the G8 summit to push their own agenda.
Tricia O'Rourke, from Oxfam, said: "The G8 have it within their power to end poverty. They can deliver on climate change. These are the people who can make a difference."