The Asian citrus psyllid, *Diaphorina citri* Kuwayama, was discovered in Florida in 1998 and is a significant pest of citrus if the pathogens that cause citrus greening disease (huanglongbing) are present. Citrus greening has recently been reported in Brazil by Fundecitrus. The establishment of *D. citri* in Florida increases the risk of the disease becoming established. *D. citri* can be distinguished from about 13 other species of psyllids reported on citrus. The biology of *D. citri* makes it well-suited to the Florida climate. Only two species, *D. citri* and *Triozas erytraeae* (del Guercio), have been implicated in the spread of citrus greening, a disease caused by highly fastidious phloem-inhabiting bacteria. The disease is characterized by mottled leaves and misshapen, poorly colored, bitter-tasting fruit. In areas where the disease is endemic, citrus trees may live for only 5-8 years and never bear usable fruit. The disease occurs throughout much of Asia, Africa south of the Sahara Desert, several small islands in the Indian Ocean, and the Saudi Arabian Peninsula. Transmission of citrus greening primarily occurs via infected psyllids and grafting, but it can also be transmitted experimentally through dodder and possibly through seeds and transovarially in psyllid vectors. Citrus greening is restricted to *Citrus* and close relatives due to the narrow host range of the psyllid vectors. Management of citrus greening is challenging and requires an integrated approach, including the use of clean stock, elimination of inoculum through voluntary and regulatory means, use of pesticides to control psyllid vectors in citrus crops, and biological control of psyllid vectors in non-crop reservoirs. There is no place in the world where citrus greening is under completely successful management. Early detection is crucial for eradication. Research is needed on rapid and robust diagnosis, disease epidemiology, and psyllid vector control.The Asian citrus psyllid, *Diaphorina citri* Kuwayama, was discovered in Florida in 1998 and is a significant pest of citrus if the pathogens that cause citrus greening disease (huanglongbing) are present. Citrus greening has recently been reported in Brazil by Fundecitrus. The establishment of *D. citri* in Florida increases the risk of the disease becoming established. *D. citri* can be distinguished from about 13 other species of psyllids reported on citrus. The biology of *D. citri* makes it well-suited to the Florida climate. Only two species, *D. citri* and *Triozas erytraeae* (del Guercio), have been implicated in the spread of citrus greening, a disease caused by highly fastidious phloem-inhabiting bacteria. The disease is characterized by mottled leaves and misshapen, poorly colored, bitter-tasting fruit. In areas where the disease is endemic, citrus trees may live for only 5-8 years and never bear usable fruit. The disease occurs throughout much of Asia, Africa south of the Sahara Desert, several small islands in the Indian Ocean, and the Saudi Arabian Peninsula. Transmission of citrus greening primarily occurs via infected psyllids and grafting, but it can also be transmitted experimentally through dodder and possibly through seeds and transovarially in psyllid vectors. Citrus greening is restricted to *Citrus* and close relatives due to the narrow host range of the psyllid vectors. Management of citrus greening is challenging and requires an integrated approach, including the use of clean stock, elimination of inoculum through voluntary and regulatory means, use of pesticides to control psyllid vectors in citrus crops, and biological control of psyllid vectors in non-crop reservoirs. There is no place in the world where citrus greening is under completely successful management. Early detection is crucial for eradication. Research is needed on rapid and robust diagnosis, disease epidemiology, and psyllid vector control.