The federal Constitution has been amended only 27 times, while the states have ratified 144 constitutions and nearly 8,000 amendments to the current 50 state constitutions. What explains the federal Constitution’s relative stability? My book argues that ongoing state constitutional revision resolves national constitutional controversies, preempting amendments to the federal Constitution and quieting conflict between the branches of the federal government. State constitutional reform guides American political development. I defend the claim with original datasets of all 12,000 proposed federal constitutional amendments and all 412 state constitutional revision bodies from 1776-2020, backed by chronological case studies of state constitutional revision. I argue this frequent, popular revision grants the state constitutions a democratic legitimacy that the national Constitution lacks.