The book's purpose is to explain from the development of life on earth to the evolution of diversity. It is this diversity that led, almost automatically to the development of pathogens and predators. The relationship of pathogens and host lead to the development of antibiotics and resistance mechanism. Man has extended this process and we now have situation in which new antibiotics only are effective for a short time. If we are to create long term antibiotics we must design them with this history in mind. Understanding antibiotic chemotherapy at the ecological level is necessary for more permanent advances in development and in the usage of antibiotic agents both old, new, and in the future. This book is indented for students at various levels that will be the microbiology researchers in the time to come. Also microbiology professors, particularly those teaching medical microbiology as well as physicians administrating antibiotics daily and researchers in the pharmaceutical industry may find this book useful.