An invasive species (alternatively known as an alien, exotic, injurious, introduced or naturalised, non-native, nonindigenous, nuisance, or noxious species) refers to an animal or plant that is introduced into an environment where it is not native. The introduction of invasive species to the United States -- whether deliberate or unintentional -- rom around the globe can pose a significant threat to native animal and plant communities, and may result in extinctions of native animals and plants, species disruptions as native and non-native species compete for limited resources, reduced biodiversity, and altered terrestrial or aquatic habitats. This can result in a range of economic, ecologic, and cultural losses, including reduced agricultural output from U.S. farms and ranches; degradation of U.S. waterways, coastal areas, national parks, and forests; and altered urban, suburban, and rural landscapes. Very broadly, the unanswered question regarding invasive species concerns whose responsibility it is to ensure economic integrity and ecological stability in response to the actual or potential impacts of invasive species, and at what cost. As this book shows, the current answer is not simple. It may depend on answers to many other questions: Is the introduction deliberate or accidental? Does it affect agriculture? By what pathway does the new species arrive? Is the potential harm from the species already known? Is the species already established in one area of the country? Finally, if the answers to any of these questions are unsatisfactory, what changes should be made? This book outlines the nature of the invasive species threat, the ability to predict invasions, methods of pest prevention or control, gaps in regulation, and options for congressional action.