An "invasive" species (alternatively known as an alien, exotic, injurious, introduced or naturalised, non-native, non-indigenous, 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 -- from around the globe can pose a significant threat to native animal and plant communities. It 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 book provides an overview of the federal laws and directives in the United States that govern invasive species, and the role of selected federal agencies. This book also examines the Lacey Act which addresses illegal wildlife trade to protect species at risk and bars importing species found to be injurious to the United States.