The diverse groups of bacteria in close association with roots and capable of stimulating plant growth by any mechanism(s) of action are referred to as plant growth-promoting rhizobacteria (PGPR). They affect plant growth and development directly or indirectly either by releasing plant growth regulators (PGRs) or other biologically active substances, altering endogenous levels of PGRs, enhancing availability and uptake of nutrients through fixation and mobilization, reducing harmful effects of pathogenic microorganisms on plants and/or by employing multiple mechanisms of action. Recently, PGPR have received more attention for use as a biofertilizer for the sustainability of agro-ecosystems. Selection of efficient PGPR strains based on well-defined mechanism(s) for the formulation of biofertilizers is vital for achieving consistent and reproducible results under field conditions. Numerous studies have suggested that PGPR-based biofertilizers could be used as effective supplements to chemical fertilizers to promote crop yields on sustainable basis. Various aspects of PGPR biotechnology are reviewed and discussed.