Knowledge of downy mildew pathogens and diseases has increased significantly in taxonomy, phylogeny, genetics, molecular biology, host-parasite interactions, ecology, epidemiology and control. The opportunity to update comprehensively the major advances in these areas was created by the 2nd International Symposium on Downy Mildews held in July 2007 at Olomouc (Czech Republic). Keynote contributions from this meeting are published here in 14 chapters that provide the most authoritative and recent analysis of these biotrophic plant pathogens and their interactions with plants. It will be an invaluable resource to students and researchers in plant pathology, mycology, taxonomy, plant biology and crop protection.