Modern agriculture relies on the extensive use of chemicals to combat plant diseases and increase agricultural productivity which leads to health and environmental hazards. In the recent past, soil microorganisms, such as the plant growth promoting bacteria (PGPB) or rhizobacteria (PGPR), have emerged as a promising tool for eco-friendly alternatives to reduce or replace the application of synthetic fertilizers and pesticides for a more sustainable crop production. PGPB/PGPR are involved in several mechanisms including nutrient cycling, alleviation of biotic/abiotic stress, hormone synthesis and soil bioremediation. In this chapter, an overview on the PGPB/PGPR roles is reported, with special focus on the mechanisms involved in PGRB/PGPR-mediated mitigation of abiotic and biotic stress in plants and their interaction with other components of the rhizosphere, i.e., the arbuscular mycorrhizal fungi (AMF).