Book excerpt: This book is part of the Plant Pathology in the 21st Century Series, started in the occasion of the IX International Congress of Plant Pathology, Torino, 2008. In conjuction with the Xth International Congress of Plant Pathology, held in Beijing in August 2013. Although deriving from a Congress, the book will not have the format of traditional Proceedings, but will be organized as a resource book. It will be based on invited lectures presented at the Congress as well as by other chapters selected by the editors among offered papers. This book will cover a topic very important in the field of plant pathology, dealing with detection and diagnostics. This field of research is continuously moving forwards, due to innovation in techniques. The application of new detection and diagnostic technologies are relevant to many applied fields in agriculture. The different chapters will provide a very complete figure of the topic, from general and basic aspects to practical aspects.