The diagnosis of infectious agents in humans and animals and the detection of pathogens in food and water are not without problems and often difficult to validate. The methods currently in use range from simple, easily managed, and routine techniques to extremely complex cutting edge technologies of modern molecular biology and high-throughput miniaturized methods. There is a clear need for rapid, accurate, and unambiguous results. This volume considers the principles behind such diverse methods and describes in some detail how diagnostic and detection methods are employed. The first section of this book discusses prions, viruses, protozoa, and helminth parasites both in host organisms and in food, drinking water and the environment. The second part focuses on future trends in diagnosis by examining emerging pathogens, the risk assessment of water-borne pathogens, and the development of exciting new micromethods.