Since the introduction of hydrilla (Hydrilla verticil/ata (L. fil.) Royle) to the United States, in Florida in the 1950s, its spread has been rapid. By 1961 it was considered a serious nuisance plant throughout central and south Florida (HaIler 1978). Hydrilla spread to the neighboring south- eastern states, reaching Louisiana by 1973 and Texas by 1974. It was discovered in California in 1976 and, later, along the eastern U.S. seaboard, with populations found in North Carolina in 1979 and in Delaware in 1981. During 1982, a monoecious biotype was reported from the Potomac River, near Washington, DC. In recent years, managers and researchers have begun a search for alternatives to conventional treatments such as herbicides. One alternative management strategy is the use of host-specific biological control agents. This research initiative was officially begun in 1980 when the U.S. Department of Agriculture, Agricultural Research Service (USDA, ARS), and the U.S. Army Corps of Engineers entered into an informal cooperative effort to identify and develop bio-control agents of hydrilla. To date, this effort has resulted in the release of four insect biocontrol agents in the United States for managing hydrilla. This article summarizes the life histories and biologies of these four insects, discusses their status and predicted impact, and describes the future direction of the hydrilla biocontrol program.