As conventionally understood, regulatory takings doctrine protects property owners from the most significant costs of legal transitions. Legal change has therefore always been central to regulatory takings claims. This Article argues that it does not need to be, and that governments can violate the Takings Clause by failing to act in the face of a changing world. This is much more than a minor refinement of takings law because government liability for failing to act means that, in at least some circumstances, the Takings Clause imposes an affirmative obligation on the government to protect property. This liability runs counter to conventional understandings of constitutional law in which the Constitution enshrines primarily negative liberties. The Takings Clause, then, can serve as a previously unrecognized basis for affirmative government obligations. The Article ultimately illustrates this new category of passive takings with the example of sea level rise, arguing that ecological threats may compel the government to respond or else face takings liability.