Detection of microbes via plant surveillance systems is channelled into the appropriate immune responses through intracellular signal transduction networks. After receptor-mediated recognition of microbe-associated molecular patterns (MAMPs), ion fluxes are induced at the plasma membrane. This is tightly linked to an increase in cytoplasmic calcium levels, which is perceived by calcium sensing proteins and accompanied by activation of protein kinases such as CDPKs (calcium-dependent protein kinases) and MAPKs (mitogen-activated protein kinases), ROS (reactive oxygen species) production, and ultimately expression of defence genes as well as accumulation of defence molecules. The temporally and spatially fine-tuned defence response calls for an integrative coordination of all these subsets of signalling events. Pathogens, on the other hand, have evolved effectors (E) that subvert plant signalling and interfere with immunity-related defence. Using model plant systems such as Arabidopsis thaliana, our research focuses on unravelling the early plant cellular signalling network and the interplay with pathogen effectors.