Over the past 70 years, the free-floating aquatic fern Salvinia molesta D.S. Mitchell (giant salvinia) has spread from its native range in Brazil to many tropical and subtropical regions. Though innocuous within its native range, elsewhere this species is an aggressive menace that has had devastating ecological and socioeconomic impacts on aquatic systems in parts of Africa, Sri Lanka, India, Australia, New Guinea, and the Philippines. In the United States, the plant is established in waterways in at least 10 states (mainly in the south) and is expected to continue to expand in areas generally where Eichhornia crassipes (Mart.) Solms (water hyacinth) persists. Listed as a Federal Noxious Weed since 1984, S. molesta is prohibited from importation to the United States and from transport across state lines. Dense mats of S. molesta can suppress growth of native vegetation and degrade water quality, fish and wildlife habitat, and numerous other ecological values. Notably, massive infestations have occurred in the Swinney Marsh Complex, Texas, in the Lower Colorado River, Arizona/California, and in Lake Wilson and Enchanted Lake, Hawaii. This report presents a review of available information on the growth, distribution, and ecology of S. molesta. Information is provided on the plant's taxonomic status, its field characteristics, phenology, and spread overseas and in the United States. Growth responses of S. molesta in relation to environmental variables (e.g., temperature, nutrients, light, pH, conductivity) are emphasized as are impacts of the species on the environment and other aquatic organisms Different technologies (i.e. physical chemical biological and integrated) applied to control S. molesta infestations are discussed along with information on the effectiveness of these procedures and their need for further study.