Abstract: I calculate the restrictions to fixed points of a basis of the equivariant cohomology of Bott-Samelson varieties, and I give a description by generators and relations of these cohomology algebras. I describe the link between the cohomology of Bott-Samelson varieties and the cohomology of flag varieties. I use these results to give a method to calculate the structure constants of the equivariant cohomology of the flag varieties (equivariant Schubert calculus).