A brief history of the Poincare conjecture

In 1904 H. Poincare proposed the problem of deciding whether a closed simply connected 3-manifold exists which is not homeomorphic to the 3-sphere. A negative answer to the question was soon labeled as the Poincare conjecture, although Poincare himself made no attempt to answer it. The question puzzled mathematicians for over 100 years and finally a positive answer to the conjecture has recently been obtained by G. Perelman. As many of the problems remained open for a long time, Poincare conjecture or, better, the attempt at a deeper understanding of the problem produced an incalculable amount of mathematics. The aim of this essay is to give a report, short and incomplete of necessity, of some of those developments as well as brief comments on still open problems.