The literature on America’s unwritten constitution is rigorous and compelling, but it tends to focus almost entirely on how the federal Constitution has evolved through informal processes. In this chapter, I argue that our understanding of America’s unwritten constitution would be improved if we broadened the inquiry to include state constitutions. Unlike the federal Constitution, where Article V’s near-impossible amendment rules force essentially all reforms into informal pathways, the states have designed amendment rules and facilitated political cultures that encourage frequent formal amendment of constitutional text. Consequently, to the extent that unwritten constitutional commitments exist in the states, they are not the product of necessity, and they may shed new light on how constitutional rules evolve. In this chapter, I show that in various significant areas, states have indeed fostered robust unwritten constitutions and that state constitutionalism is characterized by a complex, competitive, and highly contextual interaction between codified and unwritten constitutional commitments.