What was Jürgen Trittin's business in Chantilly, US in 2012? His fellow Green party members demanded of him at the time. The question itself revealed a certain amount of dissatisfaction, because the answer was well-known: the Green parliamentary party leader had attended the Bilderberg conference.

This was viewed as an affront to the party. A left-winger participating in a secret wheeling-and-dealing forum for the rich and powerful - it was unheard of. Trittin, casting around for an explanation, pointed out that green opinions had to be represented in particular where they were not yet getting the support of a majority.

Shrouded in mystery, elitist, secretive

Trittin had some explaining to do after he returned from the summit

Bilderberg attendees subject themselves to specific rules of participation. The most important one is known as the "Chatham House Rule" (in place since 1927, established at the time by the Royal Institute of International Affairs) and obliges every conference attendee to observe absolute confidentiality with respect to conversation content and speakers' statements. Unsurprisingly, this meeting point of the power wielders draws criticism year after year (the 2015 conference starts on Thursday, 11 June, and ends on Sunday, 14 June), due to its lack of transparency.

Organizers and participants contend that these are rare occasions for global decisionmakers to speak freely, for the meeting - which does see journalists among the attendees time and again - does not allow any media reporting. It's a closed shop event.

There is little information on exactly what is happening at Bilderberg conferences - and it is unspectacular to boot. Participants give explanations and argue with each other, in 90-minute intervals. Two years back, in "The Grove," a luxury resort north of London, one attendee described the food as nothing special: typical buffet catering, with everyone having to pay for the accompanying wine from their own pockets.

Every conspiracy theorist's favorite

According to reports, riesling wine and roast beef provide the backdrop for nothing less than saving the world. According to the memoir of George McGhee, a former US ambassador to Germany, the Bilderberg round-table was instrumental in setting up the Rome treaties, a very early stage of today's European Union.

Etienne Davignon, Belgian entrepreneur and Bilderberg honorary chairman, even claims that the circle set the stage for the birth of the euro. And, time and again, questions emerge, seemingly out of nowhere: Who was behind the 1973 oil crisis, how did the German reunification come about? Conspiracy theorists have a field day.

No one gets in - unless they're allowed to

Since its inception, critics of the Bilderberg conference have offered a wide range of interpretations regarding the core of the event. According to media sociologist Rudolf Stumberger, the noble gathering amounts to an attempt at re-feudalization. Dutch political scientist Kees van der Pijl believes that interests represented at the conference have little to do with democracy.

However, in its seventh decade, the fascination of the secret Bilderberg circle appears to be unabated. "Fraternizing with some of the most influential people in the world," British actor Ian Richardson wrote in 2011, "serves as an extraordinary psychologicial aphrodisiac."

How it all started

That must already have been the case at the time of the first meeting of this kind, in 1954. The venue for the premiere - which, henceforth, gave the conference its name - was the "Hotel de Bilderberg," located in Oosterbeek in the Netherlands. For the first 20 years, Prince Bernhard performed chairperson duties, until he had to step down as a result of his involvement in a corruption scandal surrounding arms manufacturer Lockheed. That was perfect fodder for the critics, who have always placed Bilderbergers under general suspicion, because of the alleged links between politics and business.