There are three types of regulatory takings. The first is the physical invasion taking where a claim for inverse condemnation is made when the government enters or allows others to enter, your property. The leading physical invasion case is Loretto v. Teleprompter Manhattan CATV Corp., 458 U.S. 419 (1982), where a landlord in New York was required to take a shoebox-sized junction box for a cable system on the roof of her apartment building. The U.S. Supreme Court held that even the smallest physical invasion taking is compensable. The test for a physical invasion taking is the simplest of all: if the government physically takes your property, they have to pay for it. Period. End of discussion. We call it the per se test.
The second type of taking, hardly ever seen, is a hybrid between the partial taking caused by overregulation and the Loretto-style physical invasion taking. These are called “categorical takings,” and the leading case is Lucas v. South Carolina Coastal Council, 505 U.S. 1003 (1992). David Lucas had two oceanfront lots in South Carolina, and the government told him that there was no way it would ever allow him to develop. The government also conceded that the property had no economic use as a consequence. Lucas sued and eventually made his way to the U.S. Supreme Court. The Court announced this new variant, the categorical taking, where property is rendered valueless as a result of government regulation. The test in Lucas, just like the one Loretto, is simply if your property is rendered valueless, the government has to write a check.
But nearly all inverse condemnation cases arise out of partial regulatory takings, as when a developer is required to set aside some large amount of open space in return for getting a subdivision approval or is permitted only a few townhouse units on a property that could easily be developed with 50 or more. In the most famous and first partial regulatory takings case, Pennsylvania Coal Co. v. Mahon, 260 U.S. 393 (1922), Justice Holmes offered the rule that launched an untold number of lawsuits and thousands of articles by tenure-seeking academics: “the general rule at least is that while property may be regulated to a certain extent, if regulation goes too far it will be recognized as a taking.”