Encarsia formosa is a parasitoid used worldwide for the biological control of whiteflies on vegetables and ornamental plants grown in greenhouses. Because of outstanding success in controlling Trialeurodes vaporariorum on tomatoes, the biology and behavior of this wasp have been intensively studied to identify attributes that contribute to successful biological control and how best to manipulate augmentative releases into greenhouses to suppress whitefly population growth. In this article, we review the biology of adult and immature E. formosa, population dynamics of whitefly-parasitoid interactions, and commercial use in greenhouses. Deficits in knowledge of aspects of E. formosa's biology and use are noted.