This authored book collates information on extremophilic microorganisms from around the world with special emphasis on India. The main focus of this book is to describe extreme environments as the habitats of these microorganisms, mechanisms of the extremophiles to cope up with the surrounding environment, new taxa created, their physiological properties, their biotechnological potential in the production of different biomolecules and biomaterials, and their role in sustainability. The concept of the book is to have comprehensive information on the diversity of microorganisms in one place. The purpose of the present book is to make aware young researchers of the attempts made so far to isolate these different microbes, inspire them to revisit the extreme environments, investigate their biodiversity using advanced molecular techniques and explore further their biotechnological potential. This book is of interest to post-graduate students, young researchers of India as well as other countries. It is useful reading material for researchers involved in environmental microbiology, microbial diversity, microbial systematics, microbial culture collections, molecular taxonomy, and microbial biotechnology.