  This is my Habilitation a Diriger des Recherches (French thing). In this
paper I summarize the work I have done to realize the program of Witten called
-non abelian localization-. This work deals first with problems of localization
in equivariant cohomology. The second part of this paper concerns the
Guillemin-Sternberg problem -Quantization commutes with reduction- in the
geometric quantization procedure.
