This article introduces a new method, qualitative comparative analysis (QCA), to the study of state policy choice and the role of ideas in politics. The authors hypothesize an important role for normative beliefs in state policy choice even for policies that go beyond traditional subjects of “morality” policy. Specifically, the authors find that “precautionary norms” are influential determinants of recent state environmental policies regulating chemicals, even in the face of significant economic impacts. They conclude that these results offer new theoretical ideas relevant to the state innovation and diffusion literature as well as the study of ideas in the policy process.