Bacteria are single-celled microorganisms which lack nuclear membranes. They are metabolically active and divide using the techniques of binary fission. Bacteria are simple forms of life which have a highly adaptable nature. Pathogenic bacteria are those varieties of bacteria capable of causing infectious diseases in humans. The branch of biology which studies the various aspects of bacteria, such as its morphology, genetics, ecology and biochemistry, is known as bacteriology. It also attempts to identify, classify and characterize various bacterial species. Koch's postulates establish the causative relationship between a disease and a microbe. The discoveries related to vaccines and antibiotics are significant advances in the field of bacteriology. This book presents the complex subject of bacteriology in the most understandable and easy-to-understand language. Most of the topics introduced herein cover the principles and practices of bacteriology. This book can prove to be an essential guide for all those interested in bacteriology.