Abstract: The Supreme Court has increasingly defined property rights that are per se exempt from regulation in the absence of compensation, most recently in Cedar Point Nursery v. Hassid (2021) and Tyler v. Hennepin County (2023). The Court claims that it can identify property rights that are categorically protected from regulation by reference to history, tradition, and precedent. Yet this approach is oddly ahistorical; it is inconsistent with the fact that property law changed dramatically over U.S. history, as well as varying tremendously among the states. It is also inconsistent with the historical context of the Founding era. At that time, both courts and legislatures thought that property law must change over time in light of “reason and common sense.” That meant rejecting remnants of feudal property rights like quit-rents and quarter-sale rights, along with primogeniture, presumptions in favor of life estates, and conveyances that did not comply with recording statutes. It also meant the invention of a new estate in land that applied only to Native nations, a novel development designed to smooth the way to dispossession of Native lands. In reality, American history and tradition evinces a living property system that evolves over time as social conditions and needs change, as conceptions of public policy evolve, and as our notions of fairness and justice develop to promote both equality and liberty norms central to constitutional rights. Regulatory takings law would be better if the courts focused, not just on “traditional” or “established” property rights, but on the reasons for regulation and whether the obligations imposed by the regulation are unfair to impose on owners without compensation. That requires attention, not just to abstract conceptions of property that are defined in an ahistorical manner, but to the ways property law changes over time and the reasons why such changes are or are not justified in the absence of compensation. Because conceptions of fairness change over time, so must both the law of property, whether common law or statutory law. Because we have a living system, constitutional law cannot justify limits on regulation without attention to the norms and values that animate the property system as it changes over time.