We discuss Calabi--Yau compactifications with background fluxes at the level of the low energy effective action. For the fluxes in the RR-sector mirror symmetry is manifest at the level of the effective action while for the fluxes in the NS-sector the compactification manifold has to be deformed.

PACS numbers: 04.50.+h, 11.25.Mj, 11.25.Sq