Useful and Interesting Web Sites

News and Information

Math articles in Quanta Magazine

Plus Magazine is an online magazine about mathematics.

Art of Problem Solving is an online community of math teachers and students of all levels from elementary school through graduate school.

Mathematical Discussions

Mathematics Stack Exchange is a question and answer site for people studying math at any level and professionals in related fields. It's 100% free, no registration required.

Math Overflow is a question and answer site for professional mathematicians.

Math Overflow is a question and answer site for professional mathematicians.

Math subreddit

Blogs

Blog of math blogs

The AMS blog on math blogs

Another list of math blogs

Blogs hosted by the American Mathematical Society

Terence Tao

The n-Category Café ;

Ars Mathematica

The Unapologetic Mathematician

Modulo Errors

A Neighborhood of Infinity

Not Even Wrong

Shtetl-Optimized

Reference

Wikipedia is an online encyclopedia with extensive coverage of mathematics, including detailed descriptions of mathematical terms and theorems. There is also a lot of information of prominent mathematicians, past and present.

PlanetMath has a mathematical encyclopedia as well as free online expository papers and books

MathWorld is a online math reference maintained by Wolfram research.

Professional Organizations

The American Mathematical Society is the leading professional society for mathematicians. You can find interesting nontechnical articles in the Notices of the AMS.

The Mathematical Association of America is another professional organization focused mostly on undergraduate math education. They have a good collection of regular online columns.

Society for Industrial and Applied Mathematics is the leading professional society for applied mathematicians working in either academia or industry.

Department of Mathematics