What "public use" has come to mean. The phrase suggests a road, a school or a reservoir, and the Supreme Court's reading is considerably wider. In Kelo v. City of New London, 545 U.S. 469 (2005), the Court explained that when it began applying the Fifth Amendment to the states at the close of the 19th century, "it embraced the broader and more natural interpretation of public use as 'public purpose'" (545 U.S. at 480). On that reading a city's integrated economic development plan qualified, even though the Court acknowledged that the condemned land was not going to be opened, at least not in its entirety, to use by the general public. It concluded that "[b]ecause that plan unquestionably serves a public purpose, the takings challenged here satisfy the public use requirement of the Fifth Amendment" (545 U.S. at 484). The decision was and remains contentious, and it is the federal rule.
The federal limit that survives is pretext. The same opinion drew a line that matters more than it is usually given credit for: "Nor would the City be allowed to take property under the mere pretext of a public purpose, when its actual purpose was to bestow a private benefit" (545 U.S. at 478). What saved the City's plan was that it was, in the Connecticut courts' words, "carefully considered", and that every judge below agreed there was no evidence of an illegitimate purpose. A taking assembled to benefit an identified private party, with the public rationale attached afterwards, is a different case.
States are free to be stricter, and the Court said so. This is the sentence to keep, because it is also the answer to every unsourced claim about how many states responded to the decision: "We emphasize that nothing in our opinion precludes any State from placing further restrictions on its exercise of the takings power. Indeed, many States already impose 'public use' requirements that are stricter than the federal baseline" (545 U.S. at 489). What eminent domain may be used for where a particular property sits is therefore a question of that state's constitution and statutes, and the federal decision sets a floor rather than a ceiling.
What an owner is entitled to, when federal money is involved. Congress wrote acquisition policies into the Uniform Relocation Assistance and Real Property Acquisition Policies Act. Under 42 U.S.C. 4651, heads of federal agencies are to be guided "to the greatest extent practicable" by policies that include making "every reasonable effort to acquire expeditiously real property by negotiation"; appraising the property before negotiations begin, with the owner or their representative "given an opportunity to accompany the appraiser during his inspection"; establishing an amount believed to be just compensation and making a prompt offer for the full amount, which "[i]n no event" may be "less than the agency's approved appraisal of the fair market value"; providing the owner "with a written statement of, and summary of the basis for" that amount; disregarding any change in value "caused by the public improvement for which such property is acquired"; not requiring the owner to surrender possession before payment or a deposit with the court; and scheduling construction so that no lawful occupant has to move "without at least ninety days' written notice". If only part of a property is taken and the remainder is an "uneconomic remnant", the agency is to offer to acquire that too.
Two qualifications on that list are essential. It binds federal agency heads, and it reaches a state or local acquisition only through 42 U.S.C. 4655, which conditions federal financial assistance on the acquiring agency's assurance that it will be guided by those policies "to the greatest extent practicable under State law". A purely local taking with no federal money in it is governed by state law, which may say more or less.
Regulation is a different category, and it has its own line. A government can reduce what a property is worth without taking it, by regulating what may be built or done there. That is the police power rather than eminent domain, and the question of when regulation goes so far that it must be paid for is a separate body of law with its own tests. Land-use regulation as a mechanism belongs with zoning; the point here is only that a restriction and a taking are analyzed differently even when the financial effect on an owner feels similar.
