This article quantifies the threats to imperiled species in the United States, focusing on habitat destruction, alien species, pollution, overexploitation, and disease. The authors analyze data from various sources to assess the relative importance of these threats. Habitat destruction is identified as the primary lethal agent, followed by the spread of alien species. The study also highlights the significant impact of alien species on imperiled plants and animals, particularly in Hawaii. Pollution, while less prevalent, is a significant threat to aquatic species. Overexploitation and disease are also noted as important factors. The authors discuss the limitations of their data and compare their findings with other studies. They conclude by emphasizing the need for active management and incentives to protect endangered species, as the current regulatory framework may not be sufficient to address the growing threats.This article quantifies the threats to imperiled species in the United States, focusing on habitat destruction, alien species, pollution, overexploitation, and disease. The authors analyze data from various sources to assess the relative importance of these threats. Habitat destruction is identified as the primary lethal agent, followed by the spread of alien species. The study also highlights the significant impact of alien species on imperiled plants and animals, particularly in Hawaii. Pollution, while less prevalent, is a significant threat to aquatic species. Overexploitation and disease are also noted as important factors. The authors discuss the limitations of their data and compare their findings with other studies. They conclude by emphasizing the need for active management and incentives to protect endangered species, as the current regulatory framework may not be sufficient to address the growing threats.