States have increasingly taken leading roles in U.S. environmental policymaking over the past two decades. As laboratories of democracy, states have developed different levels and mixes of policies to address climate change, nonpoint source pollution, alternative energy, and other challenging environmental issues. Policy scholars have sought to explain variation in state environmental policy through two primary theoretical lenses: internal determinants and regional diffusion. While our understanding of state environmental policy adoption has grown to identify which variables are most important, less is known about how these variables interact in particular states to influence policy adoption. This study examines the interactions of variables from both theories to explain how state policies for small-scale wind energy promotion were adopted in three U.S. states. Our results highlight the nuanced role of citizen ideology, which may be important in contexts at either end of the ideological spectrum but less important in the middle—where economic development is more critical. Results also indicate that interstate competition may be over environmental as well as economic leadership. Interestingly, strength of the wind resource is not necessarily correlated with policy adoption for small-scale wind energy promotion.