With ongoing climate change, the severity, frequency and duration of different abiotic stresses have threatened the agricultural productivity around the globe. Major abiotic stresses like drought and salinity have reduced agricultural land both in the arid and semiarid regions of the world. Further decline in yield is inculcated by plant pathogens. Excessive use of chemical fertilizers induced heavy metal as secondary stress. Therefore, use of environmentally friendly approach based on plant growth-promoting rhizobacteria is a promising one to alleviate the adverse effect of stresses and improve growth of plants under such conditions. These are the natural inhabitants of diverse environment an integral part of natural ecosystem and exhibit enormous plant growth promotional capabilities. They colonize plant roots, can modulate phytohormone levels and induce local and systemic mechanism in plants that offer resistance against biotic and abiotic stress factors. When applied as biofertilizers, counteract osmotic stress, oxidative stress, provide bioprotection against heavy metals thus enhance tolerance against salinity, metal toxicity and drought stress. They change heavy metal bioavailability in soil through major processes of immobilization, transformation, acidification, precipitation, chelation, complexation, redox reactions and distribution. These bacteria also affect the physiochemical properties of saline soil by increasing organic matter content, NO3-N, available P and K of the soil, and decrease in the ECe, CEC and SAR of rhizosphere soil renders the saline soil productive. This chapter provides a brief overview of PGPR-mediated stress-tolerance responses in plants and the molecular and the cellular mechanisms responsible to alleviate drought, salt and heavy metal stresses.