This collection features four peer-reviewed literature reviews on plant growth-promoting rhizobacteria in agriculture. The first chapter considers the use of plant growth-promoting rhizobacteria (PGPR) as plant biostimulants in agriculture. It considers the benefits of PGPR, such as their ability to promote plant growth and productivity under both normal and abiotic-stressed induced environments. The chapter also looks towards PGPR application as a sustainable and efficient method to enhance crop production. The second chapter reviews recent research on the use of PGPR as biofertilizers to enhance root function and improve nutrient uptake, with emphasis on their effects on root architecture, metabolism and adaptation to abiotic stress. The third chapter explores the use of microbial bio-effectors and their ability to optimise the mineral nutrition of agricultural crops. The chapter also reviews the wealth of research on the mechanism of action, applications and efficacy of key plant growth-promoting microorganisms (PGPMs). The final chapter reviews the use of plant growth-promoting bacteria (PGPB) as a biocontrol agent against invertebrate pests. The chapter analyses the effects of PGPB species against these pest types and enlists a case study on the PGPB species Pseudomonas protegens to further demonstrate this.