The designation of critical habitat under the Endangered Species Act (ESA) can result in significant and costly consequences for landowners, industry, government, and other entities—often with little if any evidence of a commensurate benefit to the species involved. In Critical Habitat and the Challenge of Regulating Small Harms, Professor Dave Owen provides a valuable contribution to assessing the role of critical habitat during consultation on federal agency actions under ESA section 7. Specifically, in reviewing and analyzing over 4,000 biological opinions, Professor Owen devotes substantial time and resources to developing a better understanding of critical habitat in formal consultation between agencies undertaking federal actions, such as issuing permits or rules or providing project funding, and the U.S. Fish and Wildlife Service (FWS) and the National Marine Fisheries Service (NMFS) (together, the Services).