Activists are seen near the Hotel Suvretta, the venue of the Bilderberg Club annual meeting according to local medias, in St. Moritz, June 9, 2011. Miro Kuzmanovic/Reuters It is the golden ticket that every self-respecting head of state, CEO, central bank chief and military commander most wants: an invite to the Bilderberg meeting .

Founded in 1954 by Prince Berhnard - father of the former queen of the Netherlands, Princess Beatrix - Bilderberg is an annual conference which the organisers say is designed to foster dialogue between Europe and North America, with between 120-150 political leaders and experts from industry, finance, academia and the media attending.

There is no detailed agenda, no resolutions are proposed, no votes are taken, and no policy statements are issued. It is instead a forum for discussion, at which ideas can be freely exchanged - as long as you promise not to disclose the details.

As a result, it has become legendary for its secrecy and fodder for conspiracy theorists: a place where masters of the universe can plot their trajectories in utmost confidence. Gerald Ford, the former US president, said in 1965 that "you don’t really belong to the organisation, one gets an invitation from the Prince."

Some people are regular attendees: Eric Schmidt, the Google chairman; George Osborne, the British chancellor; Robert Zoellick, chairman of Goldman Sachs' board of international advisers; John Sawers, the former head of MI6; and Henry Kissinger, the former Secretary of State.

Henry Kissinger Michael Loccisano/Getty Images David Petraeus, the four-star general and former director of the CIA, has managed to have his invitation for 2015 renewed – despite being sentenced in April to two years probation for sharing classified information.

Yet other people have dropped off the list this year – either because they were unable to attend, or simply not considered relevant.

Perhaps most surprising is the absence of Christine Lagarde, managing director of the IMF, who retains enormous influence. Philip Breedlove, the American general who is the Supreme Allied Commander for Europe is also a strange person to not be on the list of confirmed guests.

Bob Dudley, the chief executive of BP, was considered important enough to make the cut in 2014, but is not attending this year. The same is true of Justine Greening, Britain's international development secretary.

Bob Dudley BP Group Chief Executive, appears on stage on Day 1 at the International New York Times/Energy Intelligence Oil & Money Conference at The InterContinental Hotel on October 29, 2014 in London, England. Anthony Harvey/Getty Images for The New York Times)

Peter Mandleson, the power behind Tony Blair's throne who revelled in the nickname "Prince of Darkness", left Downing Street in 2010 and was a regular fixture at Bilderberg ever since. But he is not attending this week's gathering.

Other absences are perhaps easier to explain.

Carl Bildt, the high profile Swedish former foreign minister and prime minister, lost his job after the 2014 election, so didn't make the Bilderberg grade. The same is true of Anders Fogh Rasmussen, former Nato Secretary General.

Surprisingly few heads of state or prime ministers attend: Mark Rutte, the Dutch leader; Heinz Fischer, the Austrian president; Alexander Stubb, Finland's prime minister; and Charles Michel, his Belgian counterpart, are the only ones to travel to Austria.

Angela Merkel attended in 2005, and David Cameron in 2013 ; Prince Charles in 1986. The Queen has never attended, although Princess Beatrix of the Netherlands is a regular, given that the meeting was founded by her father.

Bill Clinton and Gerald Ford are the only US presidents to have ever been to a Bilderberg meeting – as far as we know.