The federal Endangered Species Act (ESA), along with its state counterparts, has long been a major flash point in debates over government interference with property rights. In the ESA context, the debate has had at least two parts. First, to what extent should, and to what extent does, the ESA restrict the use of privately owned land? Second, given that restrictions on land uses and other property-related activities are imposed under the ESA, to what extent does the Takings Clause of the Fifth Amendment demand compensation of the property owner? This second question—the "takings" implications of the ESA—is our subject here. Much has been written about it elsewhere as well. The court decisions described in this report illustrate the wide variety of private property impacts that may occur under the ESA—going well beyond the land-use restrictions noted above. On the other hand, the report is not a reliable indicator of the aggregate private property impacts of the ESA program. Almost certainly, many landowners who are restricted in some way under the act do not bother to sue. Of the filed suits, CRS has no systematic way of discovering those that were resolved without published decision (as by settlement or voluntary dismissal). And finally, court decisions under the Takings Clause do not exhaust the universe of decisions stemming from the ESA's private property impacts—other legal theories may be invoked also. Sections I and II of the report give background: respectively, the ESA features pertinent to the act's impacts on private property and ESA-relevant principles of Fifth Amendment takings law. Sections III through VII then offer summaries of ESA takings decisions grouped by type of property impact involved. The decisions herein comprise all those of which CRS is aware, reported and unreported (though early decisions in a case are omitted if no longer important). Of the 18 decisions reviewed, only one, Tulare Lake Basin Water Storage District v. United States , found a taking, and as discussed that decision has been undermined by a later decision of the same judge that appears to have survived appeal. However, two other cases have yet to be finally resolved and thus may or may not ultimately find a taking. Under the ESA, the possibility of private property impacts begins with "listing"—that is, when the Secretary of the Interior, through the Fish and Wildlife Service (FWS), lists a species as endangered or threatened. The Secretary of Commerce, through the National Marine Fisheries Service (NMFS, popularly called NOAA Fisheries), administers the ESA for marine species. Important here, listing is to be done "solely on the basis of the best scientific and commercial data available" to the pertinent Secretary, without reference to economic costs or private property impacts. In sharp contrast, such costs and impacts may be considered in devising agency responses to the determination of endangered or threatened status. For example, at the time of a listing, the Secretary is required, when "prudent and determinable," to designate the "critical habitat" of the species—areas essential to its conservation. A critical habitat designation is to be based both on scientific data and "economic impact and any other relevant impact," presumably allowing impacts on private property to be weighed. This distinction between listing and subsequent agency responses such as critical habitat designation was made by Congress quite deliberately. Listing and critical habitat designation trigger the ESA provisions that may interfere with private property use. Chief among these is Section 9, prohibiting certain acts in connection with endangered animals and plants. Section 9's prohibitions apply to both private and public land, and apply regardless of whether critical habitat has been designated. For endangered animals, prohibited acts include (a) the "taking" of an animal, (b) possessing, selling or transporting an animal obtained by an unlawful "take," (c) transporting an animal interstate in the course of commercial activity, and (d) selling an animal interstate, or importing/exporting same. For endangered plants, the list is narrower—we do not describe it here since there appear to be no Fifth Amendment takings decisions involving listed plants. The term "take" is a key ESA concept, not to be confused with Fifth Amendment takings. It is expansively defined by the statute to include almost any act adversely affecting a species member—including "to harass, harm, pursue, hunt, ... capture, or collect" a listed animal. Central to the ESA's impact on private land owners, the FWS defines "harm" to include indirect harm to listed species members through certain significant habitat modifications. This agency definition has been upheld by the Supreme Court as a reasonable interpretation of the statute. By general rule, the FWS has extended almost all of the endangered species prohibitions just discussed to threatened animals and plants. "Special rules," withdrawing particular threatened species from aspects of the general regime, have been promulgated for those species with atypical management needs. The NMFS, on the other hand, adopts Section 9's endangered species prohibitions for threatened species only on a case-by-case basis. "Experimental populations" of listed species generally are treated as threatened species. To minimize its constraints on economic growth, the ESA in Section 10 allows a much-used exemption from section 9's taking prohibitions. The exemption authorizes the appropriate Secretary to permit any taking incidental to, and not the purpose of, otherwise lawful activity —allowing some projects to proceed even if they harm individuals of a listed species. Such "incidental taking permits" (ITPs) may be issued to non-federal entities after the landowner submits a habitat conservation plan (HCP) including proposed mitigation measures and the considered but rejected alternatives to the proposed action. The purpose of the HCP is to ensure that the proposed action does not appreciably reduce the survival and recovery prospects of the species. In an enforcement action for violating the ESA, the statute allows an affirmative defense for offenses committed in the good faith belief that the defendant was acting to protect persons from bodily harm. The ESA makes no mention, however, of a similar defense for acts to protect property. The absence of a property-protection defense in the ESA itself has been largely offset—as to threatened species and experimental populations, but not endangered species—by administrative regulation. Another ESA provision with obvious property rights implications is Section 7. This section comes into play only when a project has a federal nexus—as when a non-federal project requires a federal permit or is being federally funded, or the federal agency itself is carrying out the project. Section 7's mandate is that each federal agency consult with the FWS or NMFS, depending on the listed species involved, to ensure that its actions are "not likely to jeopardize the continued existence of any endangered species or threatened species, or result in the destruction or adverse modification of" designated critical habitat. (Note the focus on the species , in contrast with section 9's focus on individual members of the species.) Once consulted, the FWS or NMFS must, if listed species might be affected, prepare a biological opinion to determine the actual impact of the proposed action. If "jeopardy" of species or "destruction or adverse modification" of critical habitat (see preceding quote) is found, the FWS or NMFS must suggest "reasonable and prudent alternatives" to the proposed activity that would not violate the section 7 mandate. If the agency agrees to these or other reasonable and prudent alternatives consistent with the section 7 mandate and approved by the FWS or NMFS—and if, further, any incidental takes satisfy that mandate, and other conditions are met—then the FWS or NMFS issues an incidental take statement and the activity may go forward consistent with its terms. The incidental take analysis under section 7 is the same as for section 10 ITPs, and compliance with the mitigating measures in the biological opinion confers the same exemption from section 9 prohibitions as an ITP does on non-federal entities. A federal action may be exempted from the section 7 mandate, despite the possibility of extinction, by an Endangered Species Committee of high-ranking federal officials (popularly called the God Squad). The Committee must find, among other things, that there are no reasonable and prudent alternatives to the agency action, and that the action's benefits clearly outweigh the benefits of alternatives that would conserve the species or its critical habitat. The Endangered Species Committee exemption process is generally considered burdensome and is rarely used. Several administrative reforms were adopted in the Clinton Administration, under claimed authority in the ESA, to enhance the program's flexibility in dealing with property owners. Joint FWS and NMFS policies streamlined permit procedures for small landowners, and other initiatives encouraged landowners to increase protection for listed species on their land. Under "safe harbor agreements," landowners who increase species habitat can return to baseline conditions without penalty. And "no surprises agreements" assure a landowner that if he/she implements an HCP, there will be no further costs or land use restrictions to benefit species covered by the HCP (with minor exceptions). Federal managers also attempted, where consistent with the facts, to tilt toward threatened rather than endangered designations, to allow use of the more flexible ESA provisions governing threatened species. Use of threatened status has allowed the FWS, through "special rules," to authorize takes of members of specified species causing depredations of private property (livestock, domestic animals, crops). Usually, such takes of problem animals must be carried out by government officials, rather than the aggrieved property owner. FWS regulations governing private property depredations by members of experimental populations more often allow takes by both government agents and private landowners. Despite these impact-softening mechanisms in the ESA and in administrative reforms, the act at times may frustrate the economic desires of owners of land or other property.