private nonprofit foundation dedicated to increasing and disseminating mathematical knowledge.
http://www.claymath.org/

learned society for mathematics with a nationwide membership.
http://www.lms.ac.uk/

providing results of mathematical research and development, teaching material, and information about working mathematicians and mathematical institutions.
http://www.mathnet.de/

the National High School and Junior College Mathematics Honor Society for student mathematicians and teachers across the United States.
http://www.mualphatheta.org/

national honorary mathematics society whose purpose is the promotion of scholarly activity in mathematics among students in academic institutions.
http://www.pmemath.org/

student union for students in actuarial science, econometrics and operations research & management.
http://www.vsae.nl/
