As this book makes clear, preemption is fundamentally a question of institutional choice: Should the federal government serve as the sole regulator in a particular area or should state and federal laws operate concurrently? Is the federal government alone the preferred institution to promulgate the law governing certain conduct, or does the combination of state and federal rules promise the best regulatory design? This basic question leads to two further inquiries: First, when should Congress or federal agencies choose unilateral or concurrent regulation, and second, how should courts discern this regulatory choice in specific situations? These questions are clearly intimately related. Understanding the background conceptions informing the initial regulatory choice will assist courts in interpreting the scope of federal law in the cases before them. The allocation of power among the states and the national government is the central issue of federalism, and a theory of federalism will shape the preemption decisions of regulators and courts.

This chapter seeks to illuminate the preemption question by situating it within a larger conception of federalism. An overall understanding of the relationship of federal and state authority will help to guide both federal regulators in deciding whether to preempt state law and courts in seeking to interpret the regulatory choice. First, I outline the historical evolution of the judicial understanding of federalism from the mid-nineteenth century to today.