List of United States high school mathematics competitions

National high school mathematics competitions

American Mathematics Competitions (AMC) are the largest set of national high school competitions in the United States. These exams include the AMC 10, AMC 12, AIME, and USAMO and lead up to the selection of the U.S. team for the International Mathematical Olympiad
American Regions Math League (ARML)
American High School Internet Mathematics Competition (AHSIMC)
American Scholastic Mathematics Association (ASMA)
Continental Mathematics League (CML)
Homeschool Math Contests has a chart of math contests open to individuals (homeschooled and otherwise), and also an up-to-date state-by-state list of regional meets.
Kumon Math Challenge
Mandelbrot Competition
The Math Bee hosted by the North South Foundation
Math League -- Contests with different names in different states and regions.
mathleague.org -- organizes the state high school math championships in several states.
Moody's Mega Math Challenge
Mu Alpha Theta -- hosts both local and a national competition.
National Assessment & Testing
National Online Math League (NOML) -- Formerly the Cody Bowl
Online Math League (OML)
Rocket City Math League (RCML)
UAB Math-by-Mail
United States of America Mathematics Talent Search -- an excellent competition for students learning to solve proof-oriented problems. USAMTS Homepage

High school competitions are far too numerous to list. Click on your state and nearby states to find math contests in which you can participate.