"Understanding Bacteria" is a specialized book that deals with microbiology and the fascinating diversity of simple organisms, including bacteria, viruses, archaea, algae, fungi, and protozoa. This book offers a comprehensive and interdisciplinary perspective on microbiology, which has evolved from a purely descriptive discipline to an experimental science. It highlights the advancements made in the 20th century through molecular information and demonstrates how these insights have revolutionized the understanding of microbial life. The author, S. Srivastava, who has over 35 years of experience teaching Microbial Genetics at the University of Delhi, has written this book to provide authentic and comprehensive data about the various groups of microbes. The work is a valuable resource for students and professionals engaged in cell biology, physiology, biochemistry, ecology, genetics, and biotechnology.