Direct relations between the federal government and local governments - what this article calls cooperative localism - play a significant and underappreciated role in areas of contemporary policy as disparate as homeland security, law enforcement, disaster response, economic development, social services, immigration, and environmental protection. Despite the ubiquity of this practice, a jurisprudential clash is looming that threatens this important facet of intergovernmental relations. Historically, courts have allowed local governments to invoke federal authority as a source of local autonomy, despite the prevailing view of local governments as powerless instrumentalities of the state. The Supreme Court is increasingly suggesting, howeve...