Abstract: Congressional delegation of broad lawmaking power to administrative agencies has defined the modern regulatory state. But a new form of this foundational practice is being implemented with increasing frequency: the delegation to agencies of the power to waive requirements that Congress itself has passed. It appears, among other places, as a central feature of two signature statutes of the last decade, the No Child Left Behind Act and the Patient Protection and Affordable Care Act. We call this delegation of the power to unmake major statutory provisions “big waiver.” This Article examines the basic structure and theory of big waiver, its operation in various regulatory contexts, and its constitutional and policy implications. While delegation by Congress of the power to unmake the law it makes raises concerns, we conclude the emergence of big waiver represents a salutary development. By allowing Congress to take ownership of a detailed statutory regime—even one it knows may be waived—big waiver allows Congress to codify policy preferences it might otherwise be unwilling to enact. Furthermore, by enabling Congress to stipulate a baseline against which agencies’ subsequent actions are measured, big waiver offers a sorely needed means by which Congress and the executive branch may overcome gridlock. And finally, in a world laden with federal statutes, big waiver provides Congress a valuable tool for freeing the exercise of new delegations of authority from prior constraints and updating legislative frameworks that have grown stale. We welcome this new phase of the administrative process.