Powdery mildews are ascomycete pathogens that colonize a wide range of monocotyledonous and dicotyledonous plant species. They have an obligate biotrophic lifestyle, meaning that they can only reproduce on living plant cells. Some powdery mildews, for example the barley pathogen Blumeria graminis f. sp. hordei, have a very narrow host range and can only colonize a single plant species, while others have a broader host range and can infect multiple plant hosts. To obtain first insights into the molecular basis of the obligate biotrophic lifestyle of powdery mildew fungi we have initiated next generation sequencing-based genome projects of two species that colonize dicotyledonous host plants: Erysiphe pisi, the pea powdery mildew pathogen and Golovinomyces orontii, a powdery mildew species that colonizes the dicotyledonous reference species Arabidopsis thaliana. These efforts complement the genome sequencing of Blumeria graminis f. sp. hordei, conducted by a consortium of researchers in the U.K. and France.