Book excerpt: Preemption is a doctrine of American constitutional law, under which states and local governments are deprived of their power to act in a given area, whether or not the state or local law, rule or action is in direct conflict with federal law. This book covers not only the basics of preemption but also focuses on such topics as federal mechanisms for agency preemption, implied forms of preemption, and defensive use of federal preemption in civil litigation.