Citrus is one of the leading fruit trees, producing a highly nutritional and prized fruit throughout the world. Citrus is subject to many diseases caused by different pathogens. Among which virus and virus- like pathogens are widely distributed and damaging. As emergence of new viral diseases in other species of living organisms like man and animals, similarly in plants new viruses and viroids have also been indentified as emerging pathogens. Yellow vein clearing virus (YVCV) in lemon has been recorded as new and emerging viral disease since after first reported in Pakistan by Catara et al., (1988). This monograph is an effort to study some of the biological and physical properties. This book contains the survey to record the incidence of YVCV in lemon varieties. Environmental factors influence the symptoms expression of the disease and its severity to some extent. This book also has description about transmission trials and serology for the yellow vein clearing disease.