Using several genetically developed models (N2-fixing legume nodules, arbuscular mycorrhizae, rhizospheric associations) this new book demonstrates that in order to meet the diverse environmental challenges, land plants use a variety of nutritional and defensive symbioses with bacteria and fungi. These symbioses involve the co-operative partners' developmental programs resulted in establishing the convenient niches for microbes on the plant surfaces (in rhizosphere and rhizoplane), in tissues (inter-cellular spaces, tissue cavities) and sometimes inside the cells (symbiosomes) wherein the microbial co-habitants are hosted, managed using the multiple signalling circuits and provided with the optimal conditions for expressing their host-beneficial traits (nutrition, protection from pasts and competitors).