Bacteria are prokaryotic microorganisms, which are generally a few micrometers long. They are found in the soil, acidic hot springs, water and even radioactive waste. The toxin secreted by the bacteria is termed as an exotoxin. It disrupts the normal cellular mechanism of the host, causing major damage. Exotoxins can be classified into various types such as cell surface-active, membrane damaging and intracellular. They are used for the production of vaccines and cancer treatment. The treatment of cancer involves the elimination of cancer cells without causing harm to normal cells. This is achieved by attaching an antibody or receptor ligand to the exotoxin. This results in the creation of a recombinant toxin which harms specified cells. This book traces the progress in the field of bacteriology and highlights some of its key concepts and applications. It consists of contributions made by international experts. Those in search of information to further their knowledge will be greatly assisted by this book.