Next month, more than 3,000 journalists will descend on Gleneagles, the luxury five-star hotel with its three world-renowned golf courses in the countryside 45 miles north of Edinburgh. The occasion is the G8 summit, which will dominate headlines around its start date: July 6. However, if you wanted to get in touch with this high-profile institution you’d find a very low-profile presence. There is no imposing headquarters, no rule book, no teams of permanent staff.

In fact, it’s not really an organisation at all, more of a prestigious meeting place, a travelling roadshow for global power-brokers. It doesn’t so much vote on decisions as agree on directions, using the political muscle of its membership.

“The G8 is a little hard to understand, because it doesn’t actually have a formal organisational structure or a building anywhere,” says Lael Brainard, senior fellow at the Brookings Institution in Washington and a former aide to President Clinton. “It’s really a mechanism for countries which have a very large impact on the world economy, and a role to play in co-ordinating peace initiatives, to get together regularly to act in a positive way.”

G8 is short for group of eight, the world’s richest countries, but it started out as seven. In the early 1970s, finance ministers from the United States and the bigger European allies, Britain, France, West Germany and Italy, began to meet for “fireside chats” to discuss ways to find greater currency stability. In November 1975, in the wake of the oil crisis, the first official summit, with Japan invited on board, was held at Rambouillet in France. Canada was added in 1976, making it G7.

The only other country to join was post-Communist Russia. Its inclusion has raised questions about what the G8 is meant to represent and how it should be seen in relation to more formal international organisations such as the United Nations.

These eight members dominate many other international organisations such as the European Union. Their meetings can side-step the deliberations of the United Nations. But if the UN proves problematic, four out of five of the permanent members of the Security Council are also in the G8.

The World Bank, which provides funds for development projects, has five large shareholders, all G8 members. Although the International Monetary Fund has a more broadly based governing board, its voting system gives greater weight to its biggest investors - so the G8 nations control almost 50 per cent of the votes.

“What’s very significant about the G7, and I exclude Russia from this, is that those seven economies are disproportionately influential in the international financial institutions and really do have a very powerful role,” says Ms Brainard. The G7 agreement provided the “leverage” to push through debt-relief proposals, she says.

The UN is built on tenets of inclusiveness and international law, but the G8 format has grown from “summit diplomacy”, where leaders gather to tackle specific issues. Before each summit, there are prolonged preparations: civil servants, known as sherpas, lay the path so their leaders can then take the glory as they finish the final stages of agreements.

This informal approach allows G8 leaders to get straight down to the most pressing issues: international terrorism, nuclear safety, debt relief, or post-Cold War reconstruction. But it also leaves them open to accusations of making rules for the rest of the world with no accountability.

Who asks the G8 to make its decisions? Well, no one really. Summit agendas are set by the host country. Britain, as chair this year, wants to use Gleneagles to focus on climate change and a drive to reduce poverty in Africa.

In response, environmental campaigner George Monbiot has argued that the “unregulated global capitalism” promoted by the G8 will still leave deep inequalities. “They mean it when they say they will put the poor at the top of the agenda for the G8 summit in July. The problem is that their concern for the poor ends where their concern for the rich begins.”

There have been attempts to adapt the summit system to involve more countries. After the fall of the Berlin Wall, the G24 group was set up to help develop the economies of countries that were part of the Soviet bloc.

There is also a G20 grouping, which includes countries such as China, South Africa and Brazil, and which has its own cycle of meetings.

Below the summits, there is a growing network of specialist gatherings.

This year for the first time there is a gathering for development ministers, which agreed to clamp down on the illegal logging of timber. And the G7 continues to meet separately, without Russia: finance ministers meet four times each year.

Recent summits have had more publicity for the protests that attend them: demonstrators attack them as symbols of globalisation and corporate culture. Opponents say the summits are about the rich taking decisions to further their own interests rather than the needs of the developing world and the environment. They complain that the G8 is self-appointed; you can’t make it answerable to those who disagree with its decisions.

The growth of anti-globalisation protests has turned summits into huge security operations, dominated by images of massed ranks of police and demonstrators. Okinawa in 2000 was protected by 20,000 police and security officials; at Genoa in 2001, a protester died.

Defenders say that such high-powered gatherings can deliver results.

Wealthy countries can mobilise large amounts of cash. Genoa agreed $1 billion for a fund against Aids and in 1992 the former Soviet Union was pledged $26 billion. The G8 has also provided $70 billion in debt relief for developing countries.

Without any formal voting structure, or rules for enforcing decisions, agreements are as much about setting the political mood music as about making specific changes. It’s a collective, collaborative process, rather than confrontational - and the rather bland statements that emerge permit a wide range of interpretations.

Next month, Gleneagles will be presented with action plans to help reverse sub-Saharan Africa’s cycle of poverty and deprivation. But when the summit addresses climate change, it will not be simply a case of hammering out a deal. With countries such as the US failing to adopt existing treaties on tackling greenhouse gas emissions, Gleneagles will be about “broad aims”, such as trying to achieve a scientific consensus on the relationship between emissions and climate change.

Whatever collective agreements emerge, Sir Nicholas Bayne, former diplomat and now lecturer at the London School of Economics, says there could be some “blunt but cathartic exchanges”, perhaps towards the US for its unilateralist foreign policies and Russia for its erosion of civil liberties.

The summit is going to have its own specially-designed tartan. The pattern involves the weaving of different strands, often running in different directions. It might be an appropriate symbol.

www.g8.gov.uk has a G8 history and FAQswww.g7.utoronto.ca includes an archive of G8 declarations