Understanding the Evolution of Plant Growth-Promoting RhizobacteriaPSambangiauthorVSrinivasauthorSGopalakrishnanauthorSoil is an integral part of the complicated natural environment which is very much alive with complex ecosystem of microbes. Among them, the symbiotic association of rhizobacteria with plants especially on agriculturally important crops is very much advantageous in improving the soil and plant health. These plant growth-promoting rhizobacteria (PGPR) have evolved over the years and involved in many plant functions such as growth promotion, root development, colonization, production of metabolites and in eliciting plant defence mechanism against abiotic and biotic agents. The PGPR’s ability to fix the atmospheric nitrogen, solubilize phosphate, potassium and zinc, produce siderophore along with wide variety of phytohormones and secondary metabolites such as antibiotics have attributed to their significance as biocontrol agents. These functions lead to their application as biofertilizers, biopesticides, bioprotectants and phytostimulators. The employment of these PGPR is very much important in agricultural fields as they reduce the burden of chemical fertilizers and pesticides to the farmers and in turn promises an increased crop yield. This chapter discusses the symbiotic association of PGPR with plants in detail including their direct and indirect mechanisms and basis of their induced systemic defence mechanism. It also highlights the use of bioinoculants and nanoformulations of PGPR as an effective tool towards enhanced agricultural production and to combat the plant diseases in an eco-friendly manner.AgricultureSoil2020-10SpringerBook Section