Technical Abstract: Iris yellow spot, caused by Iris yellow spot virus, is an emerging disease of onion in the U.S. and world. The disease has become pandemic in onion in the past decade, and new hosts of the virus continue to be reported. Yield losses vary depending on cultivar susceptibility and grower cultural practices, and may range from undetectable to 100% in onion seed crops. Little is known about disease epidemiology, but recent research has identified important inoculum sources of the pathogen, non-chemical practices that reduce the incidence of disease, and cultivars with moderate levels of resistance to iris yellow spot. A summary of current knowledge on disease etiology, epidemiology, and management is presented, as are prospects for future research. Successful management of iris yellow spot requires an integration of biological, cultural, and chemical control strategies to reduce disease to an economically-acceptable level.