Crazy for Math Online Contest - An annual online contest for children to share ideas on how they use math in activities with their families. - http://crazy4math.com
Mathematical Contest in Modeling (COMAP) - Annual online competition for teams of undergraduates to use mathematical modeling to solve real world problems. Includes information about registration and an archive of past contest questions. - http://www.comap.com/undergraduate/contests/mcm/
USA Mathematical Talent Search (USAMTS) - A free mathematics competition available to all high school students in the United States. Interested participants may enter the competition at any time of the academic year. - http://www.usamts.org/
ABACUS International Math Challenge - Monthly contest available in 3 age groups from 3rd grade to 8th grade. - http://www.gcschool.org/pages/program/Abacus.html
MATHmodels - A online team competition where students compete to solve real-life problems using mathematical modeling. - http://www.mathmodels.org/
International Mathematical Talent Search - A free competitive year-round correspondence program in creative mathematical problem solving at the secondary school level. Open to students in every country. - http://www.cms.math.ca/CMS/Competitions/IMTS/
Paper Challeran - A point-based puzzle contest available worldwide. Encourages arithmetic and strategy skills. - http://www5.ocn.ne.jp/~pachalle/pachalleEnglishpage.html
Online Math Madness - Browser based mathematics competition for students to gain problem solving experience. - http://www.virtu-software.com/mathmadness/