This book is devoted to the problem of the interaction between soil microorganisms and higher plants. The material presented includes basic information on the structure, development, variability and classification of bacteria, actinomycetes and fungi in the light of recent scientific achievements, as well as information on the importance of microorganisms in plant nutrition, the role of micro-activities in the complementary nutrition of plants, the effect of microbes on the vitamin content of plants, their importance in plant development and their influence on soil fertility. In addition, data are given on the importance of antibiotics as a means of therapy and prevention of diseases in agricultural practice. The book is designed for the use of microbiologists. plant physiologists, soil specialists, phytopathologists, mycologists, agrobilologists, and agronomists. It may also serve as a textbook for students In biological faculties of universities or agricultural and forestry institutes.