It is the world's most exclusive club, to which only the very brightest can hope to win entry. To join, you must demonstrate the sort of hyper-intelligence synonymous with an Einstein or Stephen Hawking. Most fall short - the failure rate for admittance is 98%.
Yet what exactly is the point of Mensa, the high-IQ society which this year celebrates its 60th birthday?
Do its members - there are over 100,000 worldwide, and some 1,200 in Ireland - come together to pore over complex mathematic challenges. Will you find them gathered around Sudoku puzzles, laughing at how easy they are?
And is it true that, celebrity members such as Brendan O'Carroll, Geena Davis and the cartoon character Lisa Simpson aside, most wear nerdish spectacles and look a little like ubergeek Bill Gates?
Nothing could be further from the truth, says David Schulman, head of Mensa Ireland. The boffin image is just a lazy stereotype, insists Schulman: "Mensa includes not only professors and doctors, but bus drivers and street cleaners - as well as the unemployed and unemployable."
What draws people to Mensa, he says, is a desire to meet others with whom they have something in common. A few, he admits, are on an ego trip. Once they realise they are not uniquely brainy "the hubris gets knocked out of them pretty fast".
Irish Mensa is only 30 years old, yet has eclipsed many of its elder siblings. It has the highest membership per head of population in the world - 162 have signed up in the past 12 months alone.
Joining Mensa can be a passport from a life of drudgery, says Schulman, who is also honorary head of Mensa International. He recalls a warehouse worker who, on becoming a member, discovered an entirely new world.
"The people he worked with were interested mostly in talking about booze and birds and he had wondered if there wasn't something wrong with him," reveals Schulman. "He went to Mensa and learned he was not alone. It transformed his life. He left the warehouse and is now training as an accountant."
Measuring brain power is far from straightforward, says Schulman. He defines intelligence as "the speed of one's cop-on", that is, the rate at which your brain assimilates and reacts to information.
"I'm talking to you right now and you are taking in the information and processing it. With another person, it might take longer for the penny to drop - that is what we mean by intelligence," he says.
Contrary to popular perception, Mensa does not have its own system of gauging mental agility. Rather, it depends on standardised IQ tests, of which there are several. The only criteria is that a candidate ranks among the top 2% for that particular test.
These tests are themselves a source of contention. Mensa tries to avoid questions that rely on previous knowledge. But some academics, including Munder Adahami, of the Centre for the Advancement for Thinking (CAT) in London, believe that repeatedly taking Mensa-approved IQ tests may improve one's performance by as much as 10%.
The organisation was founded in England in 1946 by Roland Berrill, an Australian barrister, and Lancelot Ware, an English scientist and lawyer. Their aim was a non-political society free from racial or religion distinction.
'Mensa' comes from the Latin word for table, indicating the club is to be a 'round table' for equals (it is a source of amusement in South America where 'menso' is slang for stupid).
Elitism is a charge often levelled at Mensa. Schulman rejects this: "Two per cent of the population may not sound like an awful lot. However, it works out as one in 50. Every bus that passes could contain one potential Mensa member. And our membership transcends differences of race, class, culture or religion."
Having a brain and knowing how to use it are not, Mensa acknowledges, the same thing. There are many clever people who can come across as being quite stupid, says Schulman, as they are not exploiting their talents. "Intelligence is no good unless you know how to get the most from it."
As to what Mensa members get up to when they are together, they enjoy much the same things as the rest of us.
"Once a month we might meet for a meal and go to the cinema," says Schulman. "You don't have to be in Mensa for that. But it is stimulating to be able to talk about a film with people who are intelligent and have interesting opinions."
Do members often feel brighter than those around them? "Oh, yes," says Schulman. "There are occasions when I have to modify my language because of whoever I am speaking to. Then again, that might be just because of my education and background."
Mensa holds regular tests for prospective members at locations around the country. To learn more about joining, email firstname.lastname@example.org or visit www.mensa.ie.