Citrus exocortis viroid (CEVd) is a causal agent of exocortis that belongs to the Pospoviroidae in the genus Pospiviroid. It has been reported to infect citrus, grapevines, and other non-host crops, and it was originally identified in the host Gynura aurantiaca through bio-amplification in 1972. Based on the stunting and epinasty symptoms in G. aurantiaca, it was confirmed to be an exocortis virus. Subsequently, the disease was referred to as CEVd. CEVd is a graft or mechanically transmitted disease in all citrus growing areas worldwide, and enormous sequence variants have been reported, indicating complex interactions between viroid sequences and biology. This chapter includes a description of transmission, symptomatology, epidemiology, and economic importance as well as the detection, diagnosis, and control measures for the identification and eradication of CEVd.