Mensa

"Mensa International consists of around 134,000 members, in 100 countries, in 51 national groups... Mensa is the largest and oldest high IQ society in the world." Mensa International: Organizational Structure.

"British Mensa can offer supervised tests using two separate, industry-standard tests, the Cattell III B and the Cattell Culture Fair III A.

A score which puts you in the top two per cent of the population on either of these papers would qualify you for membership of Mensa... The two papers test different types of IQ..." What is an IQ Test? | British Mensa.