- At a meeting of the American Mathematical Society in Los Angeles "Mathematical Challenges of the 21st Century" were proposed. Unlike "Hilbert's problems" from 100 years earlier, these were given by a team of 30 leading mathematicians of whom eight were Fields Medal winners.
- A prize of seven million dollars is put up for the solution of seven famous mathematical problems. Called the Millennium Prize Problems they are: versus ; The "Hodge Conjecture"; The Poincaré Conjecture; The Riemann Hypothesis; "Yang-Mills Existence and Mass Gap"; "Navier-Stokes Existence and Smoothness"; and The "Birch and Swinnerton-Dyer Conjecture".
- Grigori Perelman outlines a proof of the Riemann Hypothesis. In 2006 he is awarded a Fields Medal for the work but declines to accept it. In 2010 he also refuses the Clay prize of $1 000 000