Environmental Microbiology, besides a traditional discipline in developing fast, because of realization of its importance in industry, agriculture pharmaceutical concerns, public health, geological explorations, bioenergetics and as a mean to exploit new sources of energy useful for various purposes. The present text has been designed to outline the basic and fundamental aspects of environmental microbiology to be understood in its right perspective. It envisages to put forward a clear understanding of "what is environmental microbiology" and its widening horizons. Thus the scope of each chapter has been broadened enough to provide information on historical landmarks as well as new facts from current issues of major journals. Chapters have received special attention to make the student aware of future possibilities in environmental microbiology.