The need for the development of techniques based on the characteristics of the viral proteins and genomic nucleic acids was realized in order to detect, identify, differentiate and quantify viruses in the infected plants/planting materials with or without symptoms of infection. Immunoassays have been successfully applied for the detection of viruses in crop and weed host plant species as well as in the vectors. Nucleic acid-based techniques have been demonstrated to be the most reliable and sensitive tests for detection, identification and differentiation of viruses and viroids present in plants and planting materials.. Inclusion of numerous prools in appropriate chapters as appendix is a unique feature of this volume.