JUSTICE STEVENS, delivered the opinion of the Court.

In Pennsylvania Coal Co. v. Mahon, 260 U.S. 393 (1922), the Court reviewed the constitutionality of a Pennsylvania statute that admittedly destroyed "previously existing rights of property and contract." Id., at 413. Writing for the Court, Justice Holmes explained:

"Government hardly could go on if to some extent values incident to property could not be diminished without paying for every such change in the general law. As long recognized, some values are enjoyed under an implied limitation and must yield to the police power. But obviously the implied limitation must have its limits, or the contract and due process clauses are gone. One fact for consideration in determining such limits is the extent of the diminution. When it reaches a certain magnitude, in most if not in all cases there must be an exercise of eminent domain and compensation to sustain the act. So the question depends upon the particular facts." Ibid.

In that case the "particular facts" led the Court to hold that the Pennsylvania Legislature had gone beyond its constitutional powers when it enacted a statute prohibiting the mining of anthracite coal in a manner that would cause the subsidence of land on which certain structures were located.

Now, 65 years later, we address a different set of "particular facts," involving the Pennsylvania Legislature's 1966 conclusion that the Commonwealth's existing mine subsidence legislation had failed to protect the public interest in safety, land conservation, preservation of affected municipalities' tax bases, and land development in the Commonwealth. Based on detailed findings, the legislature enacted the Bituminous Mine Subsidence and Land Conservation Act (Subsidence Act or Act), Pa. Stat. Ann., Tit. 52, § 1406.1 et seq. (Purdon Supp. 1986). Petitioners contend, relying heavily on our decision in Pennsylvania Coal, that §§ 4 and 6 of the Subsidence Act and certain implementing regulations violate the Takings Clause, and that § 6 of the Act violates the Contracts Clause of the Federal Constitution. The District Court and the Court of Appeals concluded that Pennsylvania Coal does not control for several reasons and that our subsequent cases make it clear that neither § 4 nor § 6 is unconstitutional on its face. We agree.

I

Coal mine subsidence is the lowering of strata overlying a coal mine, including the land surface, caused by the extraction of underground coal. This lowering of the strata can have devastating effects. It often causes substantial damage to foundations, walls, other structural members, and the integrity of houses and buildings. Subsidence frequently causes sinkholes or troughs in land which make the land difficult or impossible to develop. Its effect on farming has been well documented — many subsided areas cannot be plowed or properly prepared. Subsidence can also cause the loss of groundwater and surface ponds. In short, it presents the type of environmental concern that has been the focus of so much federal, state, and local regulation in recent decades.

Despite what their name may suggest, neither of the "full extraction" mining methods currently used in western Pennsylvania enables miners to extract all subsurface coal; considerable amounts need to be left in the ground to provide access, support, and ventilation to the mines. Additionally, mining companies have long been required by various Pennsylvania laws and regulations, the legitimacy of which is not challenged here, to leave coal in certain areas for public safety reasons. Since 1966, Pennsylvania has placed an additional set of restrictions on the amount of coal that may be extracted; these restrictions are designed to diminish subsidence and subsidence damage in the vicinity of certain structures and areas.

Pennsylvania's Subsidence Act authorizes the Pennsylvania Department of Environmental Resources (DER) to implement and enforce a comprehensive program to prevent or minimize subsidence and to regulate its consequences. Section 4 of the Subsidence Act, Pa. Stat. Ann., Tit. 52, § 1406.4 (Purdon Supp. 1986), prohibits mining that causes subsidence damage to three categories of structures that were in place on April 17, 1966: public buildings and noncommercial buildings generally used by the public; dwellings used for human habitation; and cemeteries. Since 1966 the DER has applied a formula that generally requires 50% of the coal beneath structures protected by § 4 to be kept in place as a means of providing surface support. Section 6 of the Subsidence Act, Pa. Stat. Ann., Tit. 52, § 1406.6 (Purdon Supp. 1986), authorizes the DER to revoke a mining permit if the removal of coal causes damage to a structure or area protected by § 4 and the operator has not within six months either repaired the damage, satisfied any claim arising therefrom, or deposited a sum equal to the reasonable cost of repair with the DER as security.

II

In 1982, petitioners filed a civil rights action in the United States District Court for the Western District of Pennsylvania seeking to enjoin officials of the DER from enforcing the Subsidence Act and its implementing regulations. Petitioners are an association of coal mine operators, and four corporations that are engaged, either directly or through affiliates, in underground mining of bituminous coal in western Pennsylvania. The members of the association and the corporate petitioners own, lease, or otherwise control substantial coal reserves beneath the surface of property affected by the Subsidence Act. The defendants in the action, respondents here, are the Secretary of the DER, the Chief of the DER's Division of Mine Subsidence, and the Chief of the DER's Section on Mine Subsidence Regulation.

The complaint alleges that Pennsylvania recognizes three separate estates in land: The mineral estate; the surface estate; and the "support estate." Beginning well over 100 years ago, landowners began severing title to underground coal and the right of surface support while retaining or conveying away ownership of the surface estate. It is stipulated that approximately 90% of the coal that is or will be mined by petitioners in western Pennsylvania was severed from the surface in the period between 1890 and 1920. When acquiring or retaining the mineral estate, petitioners or their predecessors typically acquired or retained certain additional rights that would enable them to extract and remove the coal. Thus, they acquired the right to deposit wastes, to provide for drainage and ventilation, and to erect facilities such as tipples, roads, or railroads, on the surface. Additionally, they typically acquired a waiver of any claims for damages that might result from the removal of the coal.

In the portions of the complaint that are relevant to us, petitioners alleged that both § 4 of the Subsidence Act, as implemented by the 50% rule, and § 6 of the Subsidence Act, constitute a taking of their private property without compensation in violation of the Fifth and Fourteenth Amendments. They also alleged that § 6 impairs their contractual agreements in violation of Article I, § 10, of the Constitution. The parties entered into a stipulation of facts pertaining to petitioners' facial challenge, and filed cross-motions for summary judgment on the facial challenge. The District Court granted respondents' motion.

In rejecting petitioners' Takings Clause claim, the District Court first distinguished Pennsylvania Coal, primarily on the ground that the Subsidence Act served valid public purposes that the Court had found lacking in the earlier case. 581 F. Supp. 511, 516 (1984). The District Court found that the restriction on the use of petitioners' property was an exercise of the Commonwealth's police power, justified by Pennsylvania's interest in the health, safety, and general welfare of the public. In answer to petitioners' argument that the Subsidence Act effectuated a taking because a separate, recognized interest in realty — the support estate — had been entirely destroyed, the District Court concluded that under Pennsylvania law the support estate consists of a bundle of rights, including some that were not affected by the Act. That the right to cause damage to the surface may constitute the most valuable "strand" in the bundle of rights possessed by the owner of a support estate was not considered controlling under our decision in Andrus v. Allard, 444 U.S. 51 (1979).

In rejecting petitioners' Contracts Clause claim, the District Court noted that there was no contention that the Subsidence Act or the DER regulations had impaired any contract to which the Commonwealth was a party. Since only private contractual obligations had been impaired, the court considered it appropriate to defer to the legislature's determinations concerning the public purposes served by the legislation. The court found that the adjustment of the rights of the contracting parties was tailored to those "significant and legitimate" public purposes. 581 F. Supp., at 514. At the parties' request, the District Court certified the facial challenge for appeal.

The Court of Appeals affirmed, agreeing that Pennsylvania Coal does not control because the Subsidence Act is a legitimate means of "protect[ing] the environment of the Commonwealth, its economic future, and its well-being." 771 F.2d 707, 715 (1985). The Court of Appeals' analysis of the Subsidence Act's effect on petitioners' property differed somewhat from the District Court's, however. In rejecting the argument that the support estate had been entirely destroyed, the Court of Appeals did not rely on the fact that the support estate itself constitutes a bundle of many rights, but rather considered the support estate as just one segment of a larger bundle of rights that invariably includes either the surface estate or the mineral estate. As Judge Adams explained:

"To focus upon the support estate separately when assessing the diminution of the value of plaintiffs' property caused by the Subsidence Act therefore would serve little purpose. The support estate is more properly viewed as only one 'strand' in the plaintiff's 'bundle' of property rights, which also includes the mineral estate. As the Court stated in Andrus, '[t]he destruction of one "strand" of the bundle is not a taking because the aggregate must be viewed in its entirety.' 444 U.S. at 65. . . . The use to which the mine operators wish to put the support estate is forbidden. However, because the plaintiffs still possess valuable mineral rights that enable them profitably to mine coal, subject only to the Subsidence Act's requirement that they prevent subsidence, their entire 'bundle' of property rights has not been destroyed." Id., at 716.

With respect to the Contracts Clause claim, the Court of Appeals agreed with the District Court that a higher degree of deference should be afforded to legislative determinations respecting economic and social legislation affecting wholly private contracts than when the State impairs its own agreements. The court held that the impairment of private agreements effectuated by the Subsidence Act was justified by the legislative finding "that subsidence damage devastated many surface structures and thus endangered the health, safety, and economic welfare of the Commonwealth and its people." Id., at 718. We granted certiorari, 475 U.S. 1080 (1986), and now affirm.

III

Petitioners assert that disposition of their takings claim calls for no more than a straightforward application of the Court's decision in Pennsylvania Coal Co. v. Mahon. Although there are some obvious similarities between the cases, we agree with the Court of Appeals and the District Court that the similarities are far less significant than the differences, and that Pennsylvania Coal does not control this case.

In Pennsylvania Coal, the Pennsylvania Coal Company had served notice on Mr. and Mrs. Mahon that the company's mining operations beneath their premises would soon reach a point that would cause subsidence to the surface. The Mahons filed a bill in equity seeking to enjoin the coal company from removing any coal that would cause "the caving in, collapse or subsidence" of their dwelling. The bill acknowledged that the Mahons owned only "the surface or right of soil" in the lot, and that the coal company had reserved the right to remove the coal without any liability to the owner of the surface estate. Nonetheless, the Mahons asserted that Pennsylvania's then recently enacted Kohler Act of 1921, P. L. 1198, Pa. Stat. Ann., Tit. 52, § 661 et seq. (Purdon 1966), which prohibited mining that caused subsidence under certain structures, entitled them to an injunction.

After initially having entered a preliminary injunction pending a hearing on the merits, the Chancellor soon dissolved it, observing:

"[T]he plaintiffs' bill contains no averment on which to base by implication or otherwise any finding of fact that any interest public or private is involved in the defendant's proposal to mine the coal except the private interest of the plaintiffs in the prevention of private injury." Tr. of Record in Pennsylvania Coal v. Mahon, O. T. 1922, No. 549, p. 23.

The Pennsylvania Supreme Court reversed, concluding that the Kohler Act was a proper exercise of the police power. 274 Pa. 489, 118 A. 491 (1922). One Justice dissented. He concluded that the Kohler Act was not actually intended to protect lives and safety, but rather was special legislation enacted for the sole benefit of the surface owners who had released their right to support. Id., at 512-518, 118 A., at 499-501.

The company promptly appealed to this Court, asserting that the impact of the statute was so severe that "a serious shortage of domestic fuel is threatened." Motion to Advance for Argument in Pennsylvania Coal v. Mahon, O. T. 1922, No. 549, p. 3. The company explained that until the Court ruled, "no anthracite coal which is likely to cause surface subsidence can be mined," and that strikes were threatened throughout the anthracite coal fields. In its argument in this Court, the company contended that the Kohler Act was not a bona fide exercise of the police power, but in reality was nothing more than "'robbery under the forms of law'" because its purpose was "not to protect the lives or safety of the public generally but merely to augment the property rights of a favored few." See 260 U.S., at 396-398, quoting Loan Assn. v. Topeka, 20 Wall. 655, 664 (1875).

Over Justice Brandeis' dissent, this Court accepted the company's argument. In his opinion for the Court, Justice Holmes first characteristically decided the specific case at hand in a single, terse paragraph:

"This is the case of a single private house. No doubt there is a public interest even in this, as there is in every purchase and sale and in all that happens within the commonwealth. Some existing rights may be modified even in such a case. Rideout v. Knox, 148 Mass. 368. But usually in ordinary private affairs the public interest does not warrant much of this kind of interference. A source of damage to such a house is not a public nuisance even if similar damage is inflicted on others in different places. The damage is not common or public. Wesson v. Washburn Iron Co., 13 Allen, 95, 103. The extent of the public interest is shown by the statute to be limited, since the statute ordinarily does not apply to land when the surface is owned by the owner of the coal. Furthermore, it is not justified as a protection of personal safety. That could be provided for by notice. Indeed the very foundation of this bill is that the defendant gave timely notice of its intent to mine under the house. On the other hand the extent of the taking is great. It purports to abolish what is recognized in Pennsylvania as an estate in land — a very valuable estate — and what is declared by the Court below to be a contract hitherto binding the plaintiffs. If we were called upon to deal with the plaintiffs' position alone, we should think it clear that the statute does not disclose a public interest sufficient to warrant so extensive a destruction of the defendant's constitutionally protected rights." 260 U.S., at 413-414.

Then — uncharacteristically — Justice Holmes provided the parties with an advisory opinion discussing "the general validity of the Act." In the advisory portion of the Court's opinion, Justice Holmes rested on two propositions, both critical to the Court's decision. First, because it served only private interests, not health or safety, the Kohler Act could not be "sustained as an exercise of the police power." Id., at 414. Second, the statute made it "commercially impracticable" to mine "certain coal" in the areas affected by the Kohler Act.

The holdings and assumptions of the Court in Pennsylvania Coal provide obvious and necessary reasons for distinguishing Pennsylvania Coal from the case before us today. The two factors that the Court considered relevant, have become integral parts of our takings analysis. We have held that land use regulation can effect a taking if it "does not substantially advance legitimate state interests, . . . or denies an owner economically viable use of his land." Agins v. Tiburon, 447 U.S. 255, 260 (1980) (citations omitted); see also Penn Central Transportation Co. v. New York City, 438 U.S. 104, 124 (1978). Application of these tests to petitioners' challenge demonstrates that they have not satisfied their burden of showing that the Subsidence Act constitutes a taking. First, unlike the Kohler Act, the character of the governmental action involved here leans heavily against finding a taking; the Commonwealth of Pennsylvania has acted to arrest what it perceives to be a significant threat to the common welfare. Second, there is no record in this case to support a finding, similar to the one the Court made in Pennsylvania Coal, that the Subsidence Act makes it impossible for petitioners to profitably engage in their business, or that there has been undue interference with their investment-backed expectations.

The Public Purpose

Unlike the Kohler Act, which was passed upon in Pennsylvania Coal, the Subsidence Act does not merely involve a balancing of the private economic interests of coal companies against the private interests of the surface owners. The Pennsylvania Legislature specifically found that important public interests are served by enforcing a policy that is designed to minimize subsidence in certain areas. Section 2 of the Subsidence Act provides:

"This act shall be deemed to be an exercise of the police powers of the Commonwealth for the protection of the health, safety and general welfare of the people of the Commonwealth, by providing for the conservation of surface land areas which may be affected in the mining of bituminous coal by methods other than 'open pit' or 'strip' mining, to aid in the protection of the safety of the public, to enhance the value of such lands for taxation, to aid in the preservation of surface water drainage and public water supplies and generally to improve the use and enjoyment of such lands and to maintain primary jurisdiction over surface coal mining in Pennsylvania." Pa. Stat. Ann., Tit. 52, § 1406.2 (Purdon Supp. 1986).

The District Court and the Court of Appeals were both convinced that the legislative purposes set forth in the statute were genuine, substantial, and legitimate, and we have no reason to conclude otherwise.

None of the indicia of a statute enacted solely for the benefit of private parties identified in Justice Holmes' opinion are present here. First, Justice Holmes explained that the Kohler Act was a "private benefit" statute since it "ordinarily does not apply to land when the surface is owned by the owner of the coal." 260 U.S., at 414. The Subsidence Act, by contrast, has no such exception. The current surface owner may only waive the protection of the Act if the DER consents. See 25 Pa. Code § 89.145(b) (1983). Moreover, the Court was forced to reject the Commonwealth's safety justification for the Kohler Act because it found that the Commonwealth's interest in safety could as easily have been accomplished through a notice requirement to landowners. The Subsidence Act, by contrast, is designed to accomplish a number of widely varying interests, with reference to which petitioners have not suggested alternative methods through which the Commonwealth could proceed.

Petitioners argue that at least § 6, which requires coal companies to repair subsidence damage or pay damages to those who suffer subsidence damage, is unnecessary because the Commonwealth administers an insurance program that adequately reimburses surface owners for the cost of repairing their property. But this argument rests on the mistaken premise that the statute was motivated by a desire to protect private parties. In fact, however, the public purpose that motivated the enactment of the legislation is served by preventing the damage from occurring in the first place — in the words of the statute — "by providing for the conservation of surface land areas." Pa. Stat. Ann., Tit. 52, § 1406.2 (Purdon Supp. 1986). The requirement that the mine operator assume the financial responsibility for the repair of damaged structures deters the operator from causing the damage at all — the Commonwealth's main goal — whereas an insurance program would merely reimburse the surface owner after the damage occurs.

Thus, the Subsidence Act differs from the Kohler Act in critical and dispositive respects. With regard to the Kohler Act, the Court believed that the Commonwealth had acted only to ensure against damage to some private landowners' homes. Justice Holmes stated that if the private individuals needed support for their structures, they should not have "take[n] the risk of acquiring only surface rights." 260 U.S., at 416. Here, by contrast, the Commonwealth is acting to protect the public interest in health, the environment, and the fiscal integrity of the area. That private individuals erred in taking a risk cannot estop the Commonwealth from exercising its police power to abate activity akin to a public nuisance. The Subsidence Act is a prime example that "circumstances may so change in time . . . as to clothe with such a [public] interest what at other times . . . would be a matter of purely private concern." Block v. Hirsh, 256 U.S. 135, 155 (1921).

In Pennsylvania Coal the Court recognized that the nature of the State's interest in the regulation is a critical factor in determining whether a taking has occurred, and thus whether compensation is required. The Court distinguished the case before it from a case it had decided eight years earlier, Plymouth Coal Co. v. Pennsylvania, 232 U.S. 531 (1914). There, "it was held competent for the legislature to require a pillar of coal to be left along the line of adjoining property." Pennsylvania Coal, 260 U.S., at 415. Justice Holmes explained that unlike the Kohler Act, the statute challenged in Plymouth Coal dealt with "a requirement for the safety of employees invited into the mine, and secured an average reciprocity of advantage that has been recognized as a justification of various laws." 260 U.S., at 415.

Many cases before and since Pennsylvania Coal have recognized that the nature of the State's action is critical in takings analysis. In Mugler v. Kansas, 123 U.S. 623 (1887), for example, a Kansas distiller who had built a brewery while it was legal to do so challenged a Kansas constitutional amendment which prohibited the manufacture and sale of intoxicating liquors. Although the Court recognized that the "buildings and machinery constituting these breweries are of little value" because of the Amendment, id., at 657, Justice Harlan explained that a

"prohibition simply upon the use of property for purposes that are declared, by valid legislation, to be injurious to the health, morals, or safety of the community, cannot, in any just sense, be deemed a taking or appropriation of property . . . . The power which the States have of prohibiting such use by individuals of their property as will be prejudicial to the health, the morals, or the safety of the public, is not — and, consistently with the existence and safety of organized society cannot be — burdened with the condition that the State must compensate such individual owners for pecuniary losses they may sustain, by reason of their not being permitted, by a noxious use of their property, to inflict injury upon the community." Id., at 668-669.

See also Plymouth Coal Co., supra; Hadacheck v. Sebastian, 239 U.S. 394 (1915); Reinman v. Little Rock, 237 U.S. 171 (1915); Powell v. Pennsylvania, 127 U.S. 678 (1888).

We reject petitioners' implicit assertion that Pennsylvania Coal overruled these cases which focused so heavily on the nature of the State's interest in the regulation. Just five years after the Pennsylvania Coal decision, Justice Holmes joined the Court's unanimous decision in Miller v. Schoene, 276 U.S. 272 (1928), holding that the Takings Clause did not require the State of Virginia to compensate the owners of cedar trees for the value of the trees that the State had ordered destroyed. The trees needed to be destroyed to prevent a disease from spreading to nearby apple orchards, which represented a far more valuable resource. In upholding the state action, the Court did not consider it necessary to "weigh with nicety the question whether the infected cedars constitute a nuisance according to common law; or whether they may be so declared by statute." Id., at 280. Rather, it was clear that the State's exercise of its police power to prevent the impending danger was justified, and did not require compensation. See also Euclid v. Ambler Realty Co., 272 U.S. 365 (1926); Omnia Commercial Co. v. United States, 261 U.S. 502, 509 (1923). Other subsequent cases reaffirm the important role that the nature of the state action plays in our takings analysis. See Goldblatt v. Hempstead, 369 U.S. 590 (1962); Consolidated Rock Products Co. v. Los Angeles, 57 Cal.2d 515, 370 P.2d 342, appeal dism'd, 371 U.S. 36 (1962). As the Court explained in Goldblatt: "Although a comparison of values before and after" a regulatory action "is relevant, . . . it is by no means conclusive . . . ." 369 U.S., at 594.

The Court's hesitance to find a taking when the State merely restrains uses of property that are tantamount to public nuisances is consistent with the notion of "reciprocity of advantage" that Justice Holmes referred to in Pennsylvania Coal. Under our system of government, one of the State's primary ways of preserving the public weal is restricting the uses individuals can make of their property. While each of us is burdened somewhat by such restrictions, we, in turn, benefit greatly from the restrictions that are placed on others. See Penn Central Transportation Co. v. New York City, 438 U.S., at 144-150 (REHNQUIST, J., dissenting); cf. California Reduction Co. v. Sanitary Reduction Works, 199 U.S. 306, 322 (1905). These restrictions are "properly treated as part of the burden of common citizenship." Kimball Laundry Co. v. United States, 338 U.S. 1, 5 (1949). Long ago it was recognized that "all property in this country is held under the implied obligation that the owner's use of it shall not be injurious to the community," Mugler v. Kansas, 123 U.S., at 665; see also Beer Co. v. Massachusetts, 97 U.S. 25, 32 (1878), and the Takings Clause did not transform that principle to one that requires compensation whenever the State asserts its power to enforce it. See Mugler, 123 U.S., at 664.

In Agins v. Tiburon, we explained that the "determination that governmental action constitutes a taking, is, in essence, a determination that the public at large, rather than a single owner, must bear the burden of an exercise of state power in the public interest," and we recognized that this question "necessarily requires a weighing of private and public interests." 447 U.S., at 260-261. As the cases discussed above demonstrate, the public interest in preventing activities similar to public nuisances is a substantial one, which in many instances has not required compensation. The Subsidence Act, unlike the Kohler Act, plainly seeks to further such an interest. Nonetheless, we need not rest our decision on this factor alone, because petitioners have also failed to make a showing of diminution of value sufficient to satisfy the test set forth in Pennsylvania Coal and our other regulatory takings cases.

Diminution of Value and Investment-Backed Expectations

The second factor that distinguishes this case from Pennsylvania Coal is the finding in that case that the Kohler Act made mining of "certain coal" commercially impracticable. In this case, by contrast, petitioners have not shown any deprivation significant enough to satisfy the heavy burden placed upon one alleging a regulatory taking. For this reason, their takings claim must fail.

In addressing petitioners' claim we must not disregard the posture in which this case comes before us. The District Court granted summary judgment to respondents only on the facial challenge to the Subsidence Act. The court explained that "[b]ecause plaintiffs have not alleged any injury due to the enforcement of the statute, there is as yet no concrete controversy regarding the application of the specific provisions and regulations. Thus, the only question before this court is whether the mere enactment of the statutes and regulations constitutes a taking." 581 F. Supp., at 513 (emphasis added). The next phase of the case was to be petitioners' presentation of evidence about the actual effects the Subsidence Act had and would have on them. Instead of proceeding in this manner, however, the parties filed a joint motion asking the court to certify the facial challenge for appeal. The parties explained that an assessment of the actual impact that the Act has on petitioners' operations "will involve complex and voluminous proofs," which neither party was currently in a position to present, App. 15-17, and stressed that if an appellate court were to reverse the District Court on the facial challenge, then all of their expenditures in adjudicating the as-applied challenge would be wasted. Based on these considerations, the District Court certified three questions relating to the facial challenge.

The posture of the case is critical because we have recognized an important distinction between a claim that the mere enactment of a statute constitutes a taking and a claim that the particular impact of government action on a specific piece of property requires the payment of just compensation. This point is illustrated by our decision in Hodel v. Virginia Surface Mining Reclamation Assn., Inc., 452 U.S. 264 (1981), in which we rejected a preenforcement challenge to the constitutionality of the Surface Mining Control and Reclamation Act of 1977. We concluded that the District Court had been mistaken in its reliance on Pennsylvania Coal as support for a holding that two statutory provisions were unconstitutional because they deprived coal mine operators of the use of their land. The Court explained:

"[T]he court below ignored this Court's oft-repeated admonition that the constitutionality of statutes ought not be decided except in an actual factual setting that makes such a decision necessary. See Socialist Labor Party v. Gilligan, 406 U.S. 583, 588 (1972); Rescue Army v. Municipal Court, 331 U.S. 549, 568-575, 584 (1947); Alabama State Federation of Labor v. McAdory, 325 U.S. 450, 461 (1945). Adherence to this rule is particularly important in cases raising allegations of an unconstitutional taking of private property. Just last Term, we reaffirmed:

"'[T]his Court has generally "been unable to develop any 'set formula' for determining when 'justice and fairness' require that economic injuries caused by public action be compensated by the government, rather than remain disproportionately concentrated on a few persons." Rather, it has examined the "taking" question by engaging in essentially ad hoc, factual inquiries that have identified several factors — such as the economic impact of the regulation, its interference with reasonable investment backed expectations, and the character of the government action — that have particular significance.' Kaiser Aetna v. United States, 444 U.S. 164, 175 (1979) (citations omitted).

"These 'ad hoc, factual inquiries' must be conducted with respect to specific property, and the particular estimates of economic impact and ultimate valuation relevant in the unique circumstances.

"Because appellees' taking claim arose in the context of a facial challenge, it presented no concrete controversy concerning either application of the Act to particular surface mining operations or its effect on specific parcels of land. Thus, the only issue properly before the District Court and, in turn, this Court, is whether the 'mere enactment' of the Surface Mining Act constitutes a taking. See Agins v. Tiburon, 447 U.S. 255, 260 (1980). The test to be applied in considering this facial challenge is fairly straightforward. A statute regulating the uses that can be made of property effects a taking if it 'denies an owner economically viable use of his land . . . .' Agins v. Tiburon, supra, at 260; see also Penn Central Transp. Co. v. New York City, 438 U.S. 104 (1978)." 452 U.S., at 295-296.

Petitioners thus face an uphill battle in making a facial attack on the Act as a taking.

The hill is made especially steep because petitioners have not claimed, at this stage, that the Act makes it commercially impracticable for them to continue mining their bituminous coal interests in western Pennsylvania. Indeed, petitioners have not even pointed to a single mine that can no longer be mined for profit. The only evidence available on the effect that the Subsidence Act has had on petitioners' mining operations comes from petitioners' answers to respondents' interrogatories. Petitioners described the effect that the Subsidence Act had from 1966-1982 on 13 mines that the various companies operate, and claimed that they have been required to leave a bit less than 27 million tons of coal in place to support § 4 areas. The total coal in those 13 mines amounts to over 1.46 billion tons. See App. 284. Thus § 4 requires them to leave less than 2% of their coal in place. But, as we have indicated, nowhere near all of the underground coal is extractable even aside from the Subsidence Act. The categories of coal that must be left for § 4 purposes and other purposes are not necessarily distinct sets, and there is no information in the record as to how much coal is actually left in the ground solely because of § 4. We do know, however, that petitioners have never claimed that their mining operations, or even any specific mines, have been unprofitable since the Subsidence Act was passed. Nor is there evidence that mining in any specific location affected by the 50% rule has been unprofitable.

Instead, petitioners have sought to narrowly define certain segments of their property and assert that, when so defined, the Subsidence Act denies them economically viable use. They advance two alternative ways of carving their property in order to reach this conclusion. First, they focus on the specific tons of coal that they must leave in the ground under the Subsidence Act, and argue that the Commonwealth has effectively appropriated this coal since it has no other useful purpose if not mined. Second, they contend that the Commonwealth has taken their separate legal interest in property — the "support estate."

Because our test for regulatory taking requires us to compare the value that has been taken from the property with the value that remains in the property, one of the critical questions is determining how to define the unit of property "whose value is to furnish the denominator of the fraction." Michelman, Property, Utility, and Fairness: Comments on the Ethical Foundations of "Just Compensation" Law, 80 Harv. L. Rev. 1165, 1192 (1967). In Penn Central the Court explained:

"'Taking' jurisprudence does not divide a single parcel into discrete segments and attempt to determine whether rights in a particular segment have been entirely abrogated. In deciding whether a particular governmental action has effected a taking, this Court focuses rather both on the character of the action and on the nature of the interference with rights in the parcel as a whole — here the city tax block designated as the 'landmark site.'" 438 U.S., at 130-131.

Similarly, in Andrus v. Allard, 444 U.S. 51 (1979), we held that "where an owner possesses a full 'bundle' of property rights, the destruction of one 'strand' of the bundle is not a taking because the aggregate must be viewed in its entirety." Id., at 65-66. Although these verbal formulizations do not solve all of the definitional issues that may arise in defining the relevant mass of property, they do provide sufficient guidance to compel us to reject petitioners' arguments.

The Coal in Place

The parties have stipulated that enforcement of the DER's 50% rule will require petitioners to leave approximately 27 million tons of coal in place. Because they own that coal but cannot mine it, they contend that Pennsylvania has appropriated it for the public purposes described in the Subsidence Act.

This argument fails for the reason explained in Penn Central and Andrus. The 27 million tons of coal do not constitute a separate segment of property for takings law purposes. Many zoning ordinances place limits on the property owner's right to make profitable use of some segments of his property. A requirement that a building occupy no more than a specified percentage of the lot on which it is located could be characterized as a taking of the vacant area as readily as the requirement that coal pillars be left in place. Similarly, under petitioners' theory one could always argue that a setback ordinance requiring that no structure be built within a certain distance from the property line constitutes a taking because the footage represents a distinct segment of property for takings law purposes. Cf. Gorieb v. Fox, 274 U.S. 603 (1927) (upholding validity of setback ordinance) (Sutherland, J.). There is no basis for treating the less than 2% of petitioners' coal as a separate parcel of property.

We do not consider Justice Holmes' statement that the Kohler Act made mining of "certain coal" commercially impracticable as requiring us to focus on the individual pillars of coal that must be left in place. That statement is best understood as referring to the Pennsylvania Coal Company's assertion that it could not undertake profitable anthracite coal mining in light of the Kohler Act. There were strong assertions in the record to support that conclusion. For example, the coal company claimed that one company was "unable to operate six large collieries in the city of Scranton, employing more than five thousand men." Motion to Advance for Argument in Pennsylvania Coal Co. v. Mahon, O. T. 1922, No. 549, p. 2. As Judge Adams explained:

"At first blush, this language seems to suggest that the Court would have found a taking no matter how little of the defendants' coal was rendered unmineable — that because 'certain' coal was no longer accessible, there had been a taking of that coal. However, when one reads the sentence in context, it becomes clear that the Court's concern was with whether the defendants' 'right to mine coal . . . [could] be exercised with profit.' 260 U.S. at 414 (emphasis added). . . . Thus, the Court's holding in Mahon must be assumed to have been based on its understanding that the Kohler Act rendered the business of mining coal unprofitable." 771 F.2d, at 716, n. 6.

When the coal that must remain beneath the ground is viewed in the context of any reasonable unit of petitioners' coal mining operations and financial-backed expectations, it is plain that petitioners have not come close to satisfying their burden of proving that they have been denied the economically viable use of that property. The record indicates that only about 75% of petitioners' underground coal can be profitably mined in any event, and there is no showing that petitioners' reasonable "investment-backed expectations" have been materially affected by the additional duty to retain the small percentage that must be used to support the structures protected by § 4.

The Support Estate

Pennsylvania property law is apparently unique in regarding the support estate as a separate interest in land that can be conveyed apart from either the mineral estate or the surface estate. Petitioners therefore argue that even if comparable legislation in another State would not constitute a taking, the Subsidence Act has that consequence because it entirely destroys the value of their unique support estate. It is clear, however, that our takings jurisprudence forecloses reliance on such legalistic distinctions within a bundle of property rights. For example, in Penn Central, the Court rejected the argument that the "air rights" above the terminal constituted a separate segment of property for Takings Clause purposes. 438 U.S., at 130. Likewise, in Andrus v. Allard, we viewed the right to sell property as just one element of the owner's property interest. 444 U.S., at 65-66. In neither case did the result turn on whether state law allowed the separate sale of the segment of property.

The Court of Appeals, which is more familiar with Pennsylvania law than we are, concluded that as a practical matter the support estate is always owned by either the owner of the surface or the owner of the minerals. It stated:

"The support estate consists of the right to remove the strata of coal and earth that undergird the surface or to leave those layers intact to support the surface and prevent subsidence. These two uses cannot co-exist and, depending upon the purposes of the owner of the support estate, one use or the other must be chosen. If the owner is a mine operator, the support estate is used to exploit the mineral estate. When the right of support is held by the surface owner, its use is to support that surface and prevent subsidence. Thus, although Pennsylvania law does recognize the support estate as a 'separate' property interest, id., it cannot be used profitably by one who does not also possess either the mineral estate or the surface estate. See Montgomery, The Development of the Right of Subjacent Support and the 'Third Estate in Pennsylvania,' 25 Temple L. Q. 1, 21 (1951)." 771 F.2d, at 715-716.

Thus, in practical terms, the support estate has value only insofar as it protects or enhances the value of the estate with which it is associated. Its value is merely a part of the entire bundle of rights possessed by the owner of either the coal or the surface. Because petitioners retain the right to mine virtually all of the coal in their mineral estates, the burden the Act places on the support estate does not constitute a taking. Petitioners may continue to mine coal profitably even if they may not destroy or damage surface structures at will in the process.

But even if we were to accept petitioners' invitation to view the support estate as a distinct segment of property for "takings" purposes, they have not satisfied their heavy burden of sustaining a facial challenge to the Act. Petitioners have acquired or retained the support estate for a great deal of land, only part of which is protected under the Subsidence Act, which, of course, deals with subsidence in the immediate vicinity of certain structures, bodies of water, and cemeteries. See n. 6, supra. The record is devoid of any evidence on what percentage of the purchased support estates, either in the aggregate or with respect to any individual estate, has been affected by the Act. Under these circumstances, petitioners' facial attack under the Takings Clause must surely fail.

IV

In addition to their challenge under the Takings Clause, petitioners assert that § 6 of the Subsidence Act violates the Contracts Clause by not allowing them to hold the surface owners to their contractual waiver of liability for surface damage. Here too, we agree with the Court of Appeals and the District Court that the Commonwealth's strong public interests in the legislation are more than adequate to justify the impact of the statute on petitioners' contractual agreements.

Prior to the ratification of the Fourteenth Amendment, it was Article I, § 10, that provided the primary constitutional check on state legislative power. The first sentence of that section provides:

"No State shall enter into any Treaty, Alliance, or Confederation; grant Letters of Marque and Reprisal; coin Money; emit Bills of Credit; make any Thing but gold or silver Coin a Tender in Payment of Debts; pass any Bill of Attainder, ex post facto Law, or Law impairing the Obligation of Contracts, or grant any Title of Nobility." U.S. Const., Art. I, § 10.

Unlike other provisions in the section, it is well settled that the prohibition against impairing the obligation of contracts is not to be read literally. W. B. Worthen Co. v. Thomas, 292 U.S. 426, 433 (1934). The context in which the Contracts Clause is found, the historical setting in which it was adopted, and our cases construing the Clause, indicate that its primary focus was upon legislation that was designed to repudiate or adjust pre-existing debtor-creditor relationships that obligors were unable to satisfy. See e. g., ibid.; Home Building Loan Assn. v. Blaisdell, 290 U.S. 398 (1934). Even in such cases, the Court has refused to give the Clause a literal reading. Thus, in the landmark case of Home Building Loan Assn. v. Blaisdell, the Court upheld Minnesota's statutory moratorium against home foreclosures, in part, because the legislation was addressed to the "legitimate end" of protecting "a basic interest of society," and not just for the advantage of some favored group. Id., at 445.

As Justice Stewart explained:

"[I]t is to be accepted as a commonplace that the Contract Clause does not operate to obliterate the police power of the States. 'It is the settled law of this court that the interdiction of statutes impairing the obligation of contracts does not prevent the State from exercising such powers as are vested in it for the promotion of the common weal, or are necessary for the general good of the public, though contracts previously entered into between individuals may thereby be affected. This power, which in its various ramifications is known as the police power, is an exercise of the sovereign right of the Government to protect the lives, health, morals, comfort and general welfare of the people, and is paramount to any rights under contracts between individuals.' Manigault v. Springs, 199 U.S. 473, 480. As Mr. Justice Holmes succinctly put the matter in his opinion for the Court in Hudson Water Co. v. McCarter, 209 U.S. 349, 357: 'One whose rights, such as they are, are subject to state restriction, cannot remove them from the power of the State by making a contract about them. The contract will carry with it the infirmity of the subject matter.'" Allied Structural Steel Co. v. Spannaus, 438 U.S. 234, 241-242 (1978).

In assessing the validity of petitioners' Contracts Clause claim in this case, we begin by identifying the precise contractual right that has been impaired and the nature of the statutory impairment. Petitioners claim that they obtained damages waivers for a large percentage of the land surface protected by the Subsidence Act, but that the Act removes the surface owners' contractual obligations to waive damages. We agree that the statute operates as "a substantial impairment of a contractual relationship," id., at 244, and therefore proceed to the asserted justifications for the impairment.

The record indicates that since 1966 petitioners have conducted mining operations under approximately 14,000 structures protected by the Subsidence Act. It is not clear whether that number includes the cemeteries and water courses under which mining has been conducted. In any event, it is petitioners' position that, because they contracted with some previous owners of property generations ago, they have a constitutionally protected legal right to conduct their mining operations in a way that would make a shambles of all those buildings and cemeteries. As we have discussed, the Commonwealth has a strong public interest in preventing this type of harm, the environmental effect of which transcends any private agreement between contracting parties.

Of course, the finding of a significant and legitimate public purpose is not, by itself, enough to justify the impairment of contractual obligations. A court must also satisfy itself that the legislature's "adjustment of 'the rights and responsibilities of contracting parties [is based] upon reasonable conditions and [is] of a character appropriate to the public purpose justifying [the legislation's] adoption.'" Energy Reserves Group, Inc. v. Kansas Power Light Co., 459 U.S. 400, 412 (1983) (quoting United States Trust Co. v. New Jersey, 431 U.S. 1, 22 (1977)). But, we have repeatedly held that unless the State is itself a contracting party, courts should "'properly defer to legislative judgment as to the necessity and reasonableness of a particular measure.'" Energy Reserves Group, Inc., 459 U.S., at 413 (quoting United States Trust Co., 431 U.S., at 23).

As we explained more fully above, the Subsidence Act plainly survives scrutiny under our standards for evaluating impairments of private contracts. The Commonwealth has determined that in order to deter mining practices that could have severe effects on the surface, it is not enough to set out guidelines and impose restrictions, but that imposition of liability is necessary. By requiring the coal companies either to repair the damage or to give the surface owner funds to repair the damage, the Commonwealth accomplishes both deterrence and restoration of the environment to its previous condition. We refuse to second-guess the Commonwealth's determinations that these are the most appropriate ways of dealing with the problem. We conclude, therefore, that the impairment of petitioners' right to enforce the damages waivers is amply justified by the public purposes served by the Subsidence Act.

The judgment of the Court of Appeals is

Affirmed.