Bacteria are single celled microorganisms which lack nuclear membrane. 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 which are 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. The causative relationship between a disease and a microbe is established using Koch's postulates. Major advances in the field of bacteriology are the discoveries related to vaccines and antibiotics. This book presents the complex subject of bacteriology in the most comprehensible and easy to understand language. Most of the topics introduced herein cover the principles and practices of bacteriology. For all those who are interested in bacteriology, this book can prove to be an essential guide.