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. It has since been found in Ohio, Indiana, Maryland, Virginia, and Illinois. Efforts to contain and eventually 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. In 2003, we began studying EAB and its natural enemies in China, where it is and considered a minor and periodic forest pest. That year, we discovered Tetrastichus sp. (Hymenoptera: Eulophidae), a gregarious larval endoparasitoid. In subsequent years, we found this parasitoid plays an important role in regulating field populations of EAB at our research sites in Northeastern China. We will report our findings on Tetrastichus sp. 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.