This article examines the confusion surrounding constitutional protection of property under the substantive due process and takings clauses, using Murr as a springboard for reconsidering the substantive due process/takings distinction and asking whether the regulatory takings doctrine should remain a viable constitutional concept despite its muddled principles. While powerful reasons support treating as compensable economic regulations that are functionally equivalent to physical takings, important differences between physical and regulatory takings need to be recognized as limits to the degree of equivalence possible and therefore to the regulatory takings doctrine. A look back at the evolutionary paths of substantive due process, physical takings, and regulatory takings reveals those differences and provides some answers to questions about the regulatory takings doctrine. Defining the scope of the regulatory takings doctrine in light of those differences, especially the forgotten history of regulatory takings, should provide more consistency, help to resolve constitutional property's denominator puzzle, and allow regulatory takings to remain a viable constitutional concept.