This is the website for the National Association of Math Circles:
A Math Circle can be many things, but essentially it is a group of people who get together to have fun with mathematics. Math Circles exist for young children, older students, teachers, and professionals, and some groups involve all of the above!
There are Math Circles all over the world, and this website aims to create a directory of such circles and provide resources for students and teachers alike. Use this resource to find a Math Circle in your area; or, start one of your own!