What are the Millennium Prize Problems worth $1 million each?

Clay Mathematics Institute in Cambridge established seven Millennium Prize Problems in 2000, offering $1 million for solving each. These are among the hardest problems of the era. They are Riemann Hypothesis, P versus NP, Navier-Stokes, Hodge Conjecture, Birch and Swinnerton-Dyer Conjecture, Yang-Mills and the Mass Gap, and Poincaré Conjecture. Only Poincaré Conjecture has been officially solved.