In the area of regulatory takings, federal courts often confront issues of state law. This is because property is largely a regime of positive state law, while the Takings Clause is a federal constitutional guarantee. This Note deals with the standard of review to be applied by federal courts as to questions of state property law in the takings context. This Note explores two regulatory takings decisions by the Supreme Court—Lucas v. South Carolina Coastal Council and Stop the Beach Renourishment v. Florida Department of Environmental Protection—in which the Court conducted independent assessments of state property law. This Note argues that a more deferential standard of review, known as the fair support rule, is more appropriate for state-law issues arising in takings disputes. To arrive at this conclusion, this Note draws on principles of federalism and positivism expressed in Erie Railroad Co. v. Tompkins and by scholars in the legal process school.