Flux compactifications in string theory are being intensively studied these days because of their potential to stabilize the large moduli of compactifications. After explaining briefly how this works, we will concentrate on the geometrical aspects of flux compactifications, in particular on their back-reaction on the geometry. We will show how it is naturally described in the language of generalized complex geometry, introduced by Hitchin in 2002.

SPhT, CEA/Saclay