Mensa
Chapters, High IQ World, Mensa Education & Research Foundation (MERF), Mensa International, Mensa Online Club, Mensa Under Water, Mensans of the World Circle, TeenSIG, The Mensa Process
Genius Society
A high IQ society seeking members among scientists at the 99.5 percentile of intelligence (139 IQ/IEQ, SD=15).
Glia Society
Seeks to be a forum for the intelligent and to encourage intelligence-related research.
High IQ Society
An online community of intelligent persons.
HighPotentialsSociety
A forum for the intellectually highly gifted. Members must have an IQ of at least 132 (M=100; SD=16).
International High IQ Society
Five professional free IQ tests to qualify for membership. Members enjoy access to chat rooms, discussion forums, regular online tournaments in chess, backgammon, contract bridge, and Go, as well as difficult puzzles and brainteasers, and the ability to submit works to the quarterly online IQ Magazine.
Intertel
An organization of those with IQ scores in the 99th percentile (top 1% of the general population). The goals of the organization are to encourage meaningful intellectual fellowship, foster an exchange of ideas on any and all subjects, and to assist in research relating to high intelligence.
IQuadrivium Society
A high IQ society for those at and above the 99.9th percentile.
Mega Society
Society with an entrance requirement at the one in a million level, it's purpose is to provide members with forums and outlets for their ideas.
Ne Plus Ultra
An intellectually oriented club that seeks to gather exceptionally insightful people to discuss ideas across a variety of domains.
Pars Society
Seeks to provide a peaceful, intellectual and private forum for its members. Proof of intelligence level at or above plus 2.5 standard deviations is required for membership.
Poetic Genius Society
An organization for highly gifted individuals (99.5 percentile IQ, or the top 0.5% of the general population) who have a love of poetry. Members can submit works for publication in the organization's online journal and interact with fellow poets via a member chat forum, and a message board.
Prometheus Society
Educational, scientific, and research group for those with extreme intelligence.
SesquIQ
High IQ society. Membership active in environmentalism and research.
Smart People Society
Designed to develop synergy and to serve as a mutual support system as well as provide a forum for exchange of information and development of news and helpful ideas.
The Cerebrals Society
A society for those whose IQ falls at or above the 99.7th percentile (top 0.3% of the general population). Members interact via discussion forums and an online journal. IQ tests are available on this site.
The Intellect-Fellowship
A fellowship for intellectuals in the top 10% of society. The fellowship encourages creativity of members, publication of their works and thoughts, engagement in the functioning of the group and participation in one or more areas related to the fellowship.
Triple Nine Society
TNS is a high-IQ society which selects members at the 99.9th percentile using a number of IQ and academic aptitude tests. Journal: Vidya.