The diagnosis of infectious agents in humans and animals and the detection of pathogens in food and water are not without problems and are often difficult to validate. The methods currently in use range from rather simple, easily managed and routine techniques to the extremely complex cutting edge technologies of modern molecular biology and high-throughput miniaturised 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 part deals with the current position and considers 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.