The book examines the growth of microbiology as a tremendously expanding discipline intimately associated with human welfare.Besides basic concepts of this discipline the textbook examines the applications of microoganisms to environment, industry,medicine ,agriculture,forestry and public health.It attemps to bring all scattered updated matter on applied effects of microbial processes on human welfare in the form of a complete book.Besides students and teachers, the book should also interest those inclined to learn how microorganisms help maintain the quality of environment and human life.