This book is devoted to the family Erysiphaceae of the order Erysiphales. The taxonomy and species diversity of the powdery mildew fungi as the most important plant parasites are described. The order Erysiphales is represented by 64 species related to eight genera. Synonyms, locations, and dates of collection in Israel, as well as detailed descriptions of taxa based on morphological features obtained using light microscope and scanning electron microscope are provided.