The Endangered Species Act defines an endangered species as one at risk of extinction “throughout all or a significant portion of its range.” The U.S. Department of the Interior (DOI) has repeatedly defined “significant portion” to mean an area of the range essential to species persistence. This definition is redundant, and various iterations of the definition have been struck down in the past. At the same time, other proposals to list a species only in a portion of its range fail to satisfy the statutory requirements. This Article proposes to define “significant portion of its range” so as to allow DOI to list a species as endangered throughout its entire range based only on the risk of extinction in a portion of its range. The Article also provides a framework for understanding how past policies have failed.