Policies and norms diffuse from one country to another through four general channels: emulation, learning, competition, and coercion (Simmons et al. 2006). We intervene in this literature by arguing that these channels of diffusions are conditional on whether the recipient (diffusee) sees the sender (diffuser) as a friend or rival (in/outgroup). For example, political rivalry should amplify pressures to compete while suppressing pressures to capitulate to coercion. From this intuition, we develop a new theoretical framework and test its implications in the context of mass support for adopting the environmental policies of another country. To gain causal identification on our key independent variable—the sender country’s status as a friend/rival—we develop a novel survey experimental technique to randomize a foreign country’s rivalrous status. Our preliminary study finds initial support for our theoretical framework. Our study has broader implications for understanding how norms, ideas, and policy practices spread across borders.