Pathogens manipulate host physiology through the secretion of virulence factors (effectors) to invade and proliferate on the host. The molecular functions of effectors inside plant hosts have been of interest in the field of molecular plant-microbe interactions. Obligate biotrophic pathogens, such as rusts and powdery mildews, cannot proliferate outside of plant hosts. In addition to the inhibition of the plant's immune components, these pathogens are under particular pressure to efficiently extract nutrients from the host. Understanding the molecular basis of infections mediated by obligate biotrophic pathogens is of significance because of their impact in modern agriculture. In addition, powdery mildews serve as excellent models for obligate biotrophic cereal pathogens. Here, we summarise the current knowledge on the effectorome of the barley and wheat powdery mildews and putative molecular virulence functions of effectors. We emphasise the availability of comprehensive genomic, transcriptomic and proteomic resources and discuss the methodological approaches used for identifying candidate effectors, assessing effector virulence traits and identifying effector targets in the host. We highlight established and more recently employed methodologies, discuss limitations and suggest additional strategies. We identify open questions and discuss how addressing them with current available resources will enhance our understanding of Blumeria CSEPs.