Emerald ash borer (EAB), Agrilus planipennis Fairmaire (Buprestidae), an exotic wood-boring insect of ash trees (Fraxinus spp.), was first discovered in Michigan and Ontario in 2002. Since then, infestations have been found in Ohio, Indiana, Maryland, Virginia, and Illinois. Efforts to contain and eradicate this pest from North America are proving difficult due to the large scale of the infestation and lack of effective management tools. If eradication efforts are abandoned, biological control will be the primary management option. To this end, we began natural enemy studies in China in 2003 where EAB is native and considered a minor, periodic pest of ash. The next year, we discovered Oobius agrili (Hymenoptera: Encyrtidae), a solitary egg parasitoid of EAB, and found it plays an important role in regulating field populations of EAB in our study sites in Northeastern China. We will report our findings on O. agrili biology, its impact on EAB populations, the results of host range studies in our laboratory, and discuss its potential as a classical biocontrol agent for EAB management in North America.