The most important set of guidelines and authority for protection of species at the national level in the United States is the U.S. Fish and Wildlife Service Endangered Species Act (ESA). The U.S. ESA has many categories that can apply to species. The ones you may be most familiar with are endangered or threatened. Once a species is listed as threatened or endangered under the U.S. ESA, this law prohibits people from hurting, selling, or keeping these species. It also requires the U.S. government to protect these species (through penalties and fines), buy land that will help to protect these species, and provide funding for projects that will help a species recover from an endangered or threatened status.