This special issue contains 15 papers covering topics on: the field performance of a liquid formulation of Azospirillum brasilense on dryland wheat productivity; cadaverine production by A. brasilense and its possible role in plant growth promotion and osmotic stress mitigation; seedlings growth promotion by A. brasilense under normal and drought conditions; the ability of A. brasilense Az39 and Bradyrhizobium japonicum E109, inoculated singly or in combination, to promote seed germination and early seedling growth in maize and soyabean; the effect of Azospirillum inoculation and nitrogen fertilizer application on grain yield and on the diversity of endophytic bacteria in the phyllosphere of rice rainfed crop; the impact of Azospirillum brasilense and Pseudomonas fluorescens inoculation on the wheat yield; the influence of plant growth-promoting microorganisms on the utilization of urea-N and grain yield of paddy rice; the isolation, partial identification and application of diazotrophic rhizobacteria from traditional Indian rice cultivars; stress-responsive indole-3-acetic acid biosynthesis by A. brasilense SM and its ability to modulate plant growth; brominated phenols as auxin-like molecules; the growth promotion effect on the freshwater microalga Chlorella vulgaris by the nitrogen-fixing, plant growth-promoting bacterium Bacillus pumilus; A. brasilense PII proteins GlnB and GlnZ; the structural organization of the glnBA region of the A. brasilense genome; colonization of sugarcane plantlets by mixed inoculations with diazotrophic bacteria; and the diversity of 16S-rRNA and nifH genes derived from rhizosphere soil and roots of the endemic drought tolerant grass Lasiurus scindicus.