The communication between plants and microbes is the main topic treated in this illustrated book. The highly complex interactions of microbial communities with plants are illustrated by presenting concrete experimental studies of typical symbiosis. The text discusses the signaling within a symbiosis or the molecular differences between symbiotic and pathogenic microorganisms, the role of microorganisms in growth and development of plants or in plant protection against deleterious agents and the interactions of microbes with genetically modified plants. Further contributions are devoted to: the analysis of bacterial communities in the rhizosphere; microbial population genetics; various aspects of mycorrhizal symbiosis; functional genomic approaches and the use of microorganisms as bio-indicator of soil disturbance.