This Essay, prepared for the 2012 Brigham-Kanner Property Rights Conference, argues that social obligation theories in property generate previously unrecognized obligations on the State. Leading property scholars, like Hanoch Dagan, Greg Alexander, and Eduardo Peñalver, have argued that the institution of property contains affirmative duties to the community as well as negative rights. This Essay argues that those affirmative duties are two-way streets, and that moral bases for social obligations also generate reciprocal obligations on the State to protect property owners. The social obligation theories rely upon a dynamic not static vision of property rights. The community’s needs change, the conditions of ownership change, and the appropriate allocation of benefits and burdens within a society changes over time. Therefore, a legal obligation that is justified and permissible at the time it is enacted because it is consistent with moral obligations may become impermissible over time, even if the content of the legal obligation does not change. At the extreme, the State’s failure to respond to certain kinds of changes in the world can lead to a regulatory taking.