Plant growth promoting microorganisms (PGPM) are an important group of microbial inoculants, which exist in rhizosphere and have the ability to inhabit the root of the plants and improve their development. Their positive influence is achieved through solubilization of phosphorus, nitrogen fixation, production of plant nutrients and phytohormones, protection from pathogens and recovery from stressful environmental conditions. This is the main reason for the increasing usage of many PGPMs which formulations are commonly known as microbial fertilizers. Microbial fertilizers represent an attractive replacement for chemical fertilizers that are polluting the environment. They are used to increase the crop yield in an eco-friendly way while relying on sustainable agriculture principles. The biggest problem nowadays is the very poor quality of such products, which results in the lack of confidence and makes commercialization much more difficult. In order to increase production and hence the commercialization of microbial fertilizers, desired quality and stability should be achieved. For this reason, many researches are done in this particular field. In order to develop an optimal product, it is important to know and understand the process, including the physiology of bacteria and plants, mass multiplication technological processes as well as the existing formulation and the specific effect on the desired plant. For this purpose, the aim of this review is to indicate the significance of microbial fertilizers and their beneficial effects on the plants, as well as to give a brief survey of the different aspects of production processes with a special emphasis on mass multiplication.