Microorganisms are responsible for the manufacture of various foods of man. The biochemical reactions of microorganism helps in the process of production of foods. Microorganisms helps in several industries like medicine industry, jute industry. Hormones, Vitamins, Vaccines are also manufactured from microorganisms. They also used in Recombinant technology, cell fusion technology etc. In recent years the role of microorganisms in various environmental issue has been found a major importance and there is a potentials for future development. Hence the branch microbiology developed into a independent modern branch of science.In this book we have tried to emphasis the role of microorganisms in human welfare. Most of the chapters reflect the scientific progresses which have occur from long time.