Citrus tristeza virus (CTV) belonging to the genus Closterovirus, predominantly transmitted by aphid vector, Toxoptera citricida is one of the most destructive pathogens in most of the citrus growing countries in the world including India. CTV genome is a single-stranded positive-sense genomic RNA (gRNA) of 19.3 kb length with 12 open reading frames (ORFs) encoding at least 19 putative proteins. To detect and characterize CTV, a survey was conducted in different orchards of Kagzi lime, Khasi mandarin, Assam lemon, acid lime, rough lemon and sweet orange from North-eastern states (Assam, Arunachal Pradesh, Nagaland). This book provides a detailed study of incidence and characterization of Citrus tristeza virus in the North-eastern states of India.