Once in the constitutional wings, the Takings Clause of the Fifth Amendment today stands center stage. More than 50 takings cases have been decided by the Supreme Court since it launched the modern era of takings jurisprudence in 1978. No debate on the proper balance between private property rights and conflicting societal needs is complete without noting the Takings Clause. The Takings Clause states: "[N]or shall private property be taken for public use, without just compensation." Until the late 19 th century, this clause was applied by the Supreme Court only to condemnation : the formal exercise by government of its eminent domain power to take property coercively, upon payment of just compensation to the property owner. In such condemnation suits, there is no issue as to whether the property is "taken" in the Fifth Amendment sense; the government concedes as much by filing the action. The only question, typically, is what constitutes "just compensation." Beginning in the 1870s, the Supreme Court gave its imprimatur to a different use of the Takings Clause. When the sovereign appropriated or caused a physical invasion of property, as when a government dam flooded private land, the Court found that the property had been taken just as surely as if the sovereign had formally condemned. Therefore, it said, the property owner should be allowed to vindicate his constitutional right to compensation in a suit against the government. In contrast with condemnation actions, then, such takings actions have the property owner sue government rather than vice-versa; hence the synonym " inverse condemnation actions ." The key issue in takings actions is usually whether, given all the circumstances, the impact of the government action on a particular property amounts to a taking in the constitutional sense. Only if a taking is found does the question of just compensation arise. In 1922, in the most historically important taking decision, the Supreme Court extended the availability of takings actions from government appropriations and physical invasions of property, as described above, to the mere regulation of property use. This critical expansion of takings jurisprudence to "regulatory takings" acknowledged that purely regulatory interferences with property rights can have economic and other consequences for property owners as significant as appropriations and physical invasions. The regulatory taking concept opened up vast new legal possibilities for property owners, and underlies many of the Supreme Court's takings decisions from the 1970s on. The ascendancy of the regulatory taking concept since the 1970s is hardly surprising. Starting with the advent of comprehensive zoning in the early 20 th century, federal, state, and local regulation of private land use has become pervasive. Beyond comprehensive zoning, the past 60 years have seen explosive growth in the use of historic preservation restrictions, open-space zoning, dedication and exaction conditions on building permits, nature preserves, wildlife habitat preservation, wetlands and coastal zone controls, mining restrictions, and so on. Regulation of non-real-estate property has also proliferated. In the Supreme Court, the appointment of several conservative Justices since the 1970s has prompted a new scrutiny of government conduct vis-à-vis the private property owner. As a result of these factors, the Court since the late 1970s has turned its attention toward the takings issue with vigor. Through the 1980s and 1990s, property owner plaintiffs scored several major victories; by and large, the substantive doctrine of takings shifted to the right. In 2000-2005, however, the Court's decisions moved the analytical framework in a more government-friendly direction. The pendulum may yet be swinging again: the four takings cases decided by the Court during its 2012-2013 and 2014-2015 terms were all decided in favor of the property owner, though mostly as to narrow issues. * * * * * This report compiles only Supreme Court decisions addressing issues with special relevance to takings (inverse condemnation) actions, not those on formal condemnation or property valuation. Thus the headline-grabbing Supreme Court opinion in Kelo v. City of New London (2005), principally a formal condemnation case, is not included here. On the other hand, a scattering of substantive due process decisions is interspersed where they have been cited by the Court as authority in its takings decisions. In the interest of brevity, we mention no dissenting opinions, and almost no concurrences. Thus, the report does not reveal the closely divided nature of some Supreme Court takings opinions. The reader desiring a more analytical discussion of inverse condemnation law should consult CRS Report RS20741, The Constitutional Law of Property Rights "Takings": An Introduction , also prepared by [author name scrubbed]. In 1978, the Supreme Court ushered in the modern era of regulatory takings law by attempting to inject some coherence into the ad hoc analyses that had characterized its decisions before then. In Penn Central Transportation Co. v. New York City , infra page 10, the Court declared that whether a regulatory taking has occurred in a given case is influenced by three principal factors: the economic impact of the regulation, the extent to which it interferes with distinct (in most later decisions, "reasonable") investment-backed expectations, and the "character" of the government action. After Penn Central , ad hocery in judicial taking determinations emphatically still remains, but arguably is confined within tighter bounds. The Supreme Court's many takings decisions since Penn Central have developed the jurisprudence in each of its main areas: ripeness, takings criteria, and remedy. As for takings criteria, the Court announced several "per se taking" rules in the two decades after Penn Central — see, for example, Loretto , infra page 9, and Lucas , infra page 7. Decisions since 2000, however, have extolled the multifactor, case-by-case approach of that decision— see Palazzolo , infra page 5; Tahoe-Sierra , infra page 5; and Lingle , infra page 5. In Lingle , the Court summed up the four types of takings claims it now recognizes, in addition to those based on outright government appropriations: a plaintiff seeking to challenge a government regulation as an uncompensated taking of private property may ... alleg[e] a "physical" taking, a Lucas -type "total regulatory taking," a Penn Central taking, or a land-use exaction violating the standards set forth in Nollan and Dolan . The principle that government may "take" property in the Fifth Amendment sense merely through regulatory restriction of property use—that is, without physical invasion or formal appropriation of the property—was announced in 1922. In Pennsylvania Coal Co. v. Mahon , the redoubtable Justice Oliver Wendell Holmes wrote for the Supreme Court that a state law prohibiting coal mining that might cause surface subsidence in certain areas was a taking of the mining company's mineral estate. The first steps taken by this infant "regulatory taking" doctrine, however, were unsteady ones. Aside from making clear that regulatory takings occur only with the most severe of property impacts, the Court's opinions during this period display little in the way of principled decision-making. Moreover, the Court refused at times to part with its long-standing substantive due-process approach to testing property-use restrictions, vacillating between the two theories. The 1870s marked the Supreme Court's first clear acknowledgment that the Takings Clause is not only a constraint on the government's formal exercise of eminent domain, but the basis as well for suits by property owners challenging government conduct not attended by such formal exercise. However, until 1922 the Court believed such "inverse condemnation" suits to be confined to government appropriations or physical invasions of property. Cases involving the impacts of government water projects (flooding, reduced access, etc.) were typical. When cases involving mere restrictions on the use of property reached the Court, they were tested under due process, scope of the police power, or ultra vires theories.