Résumé
We decribe and announce some results (joint with G. Besson, L. Bessieres, M.
Boileau and J.Porti) about the geometry and topology of 3-manifolds. Most of
the article is primarily intended as an introduction for nonexperts to
geometrization of 3-manifolds, Ricci flow with surgery, and the simplicial
volume approach to collapsing theorems. In the last section, Ricci flow with
surgery on open 3-manifolds and obstructions to positive scalar curvature are
discussed.