The Proceedings of the 4th International Symposium held by the European Foundation for Plant Pathology on Diagnosis and Identification of Plant Pathogens in Bonn, Germany, from September 9th to 12th, 1996, include information on the application of classical as well as novel and innovative methods and techniques. This book gives an overview of the recent status and trends in the diagnosis and identification of viruses, bacteria and fungi in plants. It covers not only the development of methods and application of techniques but also its transformation into practice for disease-forecasting systems. The book includes 58 oral presentations and 61 poster contributions covering 6 main topics. In addition to introductory overviews of the phytosanitary implications of diagnosis in integrated crop protection, the application of classical and innovative diagnostic methods is stressed. The other contributions cover taxonomy and differentiation of plant pathogens, serological assays, nucleic acid based hybridisation techniques, disease assessment and quantification as well as disease prognosis and expert systems. This book provides information for all researchers and scientists involved in the production of healthy crop plants. It is of special interest for plant pathologists with responsibilities in the fields of plant quarantine, extension and applied diagnosis of plant pathogens as well as for those working in research and development of innovative crop protection techniques.