The advancing internationalisation of environmental politics has triggered increasing interest in factors that lead countries to participate in international environmental agreements. But do partisan differences matter for such ratification decisions? An analysis of the ratification responses of 21 OECD countries toward 64 treaties shows that partisan environmentalism matters for ratification behaviour whereas left–right differences do not play a significant role. More precisely, while the likelihood of ratification increases when overall government positions are more proenvironment, pro-environment veto players and environmental ministers are not found to play a role. These results hold against a number of controls and correcting for potential error in the measurement of party positions.
