Smale's problems

Smale's problems is a list of eighteen unsolved problems in mathematics proposed by Steve Smale in 1998 and republished in 1999. Smale composed this list in reply to a request from Vladimir Arnold, then vice-president of the International Mathematical Union, who asked several mathematicians to propose a list of problems for the 21st century. Arnold's inspiration came from the list of Hilbert's problems that had been published at the beginning of the 20th century. In his original article Smale written that he chosen the problems using three criteria: simple statement that is preferably precise, personal acquaintance with the problem and belief that solution (or just partial results) for the problem would have great importance for development of mathematics in 21st century. The four problems from Smale's list: Riemann hypothesis, Poincaré conjecture, P versus NP problem and Navier-Stokes smoothness and existence problem were later put on list of seven Millennium Prize problems by Clay Institute.