Humans have a long history of deliberately introducing terrestrial and aquatic species to new areas for agriculture, horticulture, soil conservation, sport fishing, hunting, pets, and a host of other reasons. These non-indigenous species are greatly beneficial to society, providing much of the food we eat, sustaining significant sectors of our economy, offering recreational opportunities, and serving as pets in our homes and flora in our gardens. At the same time, human activities like travel, trade, and natural habitat alteration have caused many unplanned or accidental introductions of species to new areas. The contemporary massive transformation of the natural environment and worldwide transport of people and cargo now facilitate species introductions - both deliberate and accidental - at a rate that completely overshadows natural rates of species movement (OTA 1993), and makes large-scale range expansions across mountains and oceans common. For the purposes of this report, we focus on these human facilitated movements of species - both deliberate and accidental - to new areas: throughout this report such species are referred to as non-indigenous species.