This new edition of A Textbook of Microbiology continues to provide a comprehensive coverage on the basic principles of the subject with its focus on the concepts of ecology of microorganisms. The book has been written in lucid and easily understandable language for students. Each chapter has self-test exercise at the end of the book. Besides fulfilling the needs of undergraduate students, this book would also be useful for postgraduate students as well as aspirants of various competitive examinations.