This chapter describes two important changes in state–federal relations over the past decade. First, intergovernmental disagreements increased and became more openly conflictual and partisan during the Obama Administration. Second, the repertoire of state resistance to federal policy has expanded. New administrative practices have a growing role in state opposition to federal policy. So too, does state-initiated litigation, which has succeeded by developing claims about administrative law and procedure rather than federalism or states’ rights. State resistance had the immediate effect of weakening or entirely preventing the implementation of important federal policies and unsettled major judicial doctrines about the authority of federal agencies. Although partisan roles have been reversed, this pattern of intergovernmental conflict has continued under the Trump Administration. Ongoing contention creates significant legal and policy uncertainty. In the long term, this contention may shift important administrative responsibilities from the federal government to states and localities.