All citizens, whether they are a business, individual, and/or public agencies must comply with the Endangered Species Act (ESA), which prohibits the "taking" of any listed species. Compliance may be as easy as determining that the species and/or their habitat are not present. However, for projects involving a federal nexus, a Biological Assessment (BA) is generally required. The BA entails a field investigation and report which describes the proposed project, project impacts, and the conservation measures used to avoid, minimize, and mitigate for project impacts. Businesses or landowners not requiring a federal permit may pursue a "no take" letter, or a "take avoidance" letter. Incidental take may be authorized where nonfederal parties prepare a Habitat Conservation Plan (HCP) describing their proposed actions to conserve listed species.