This paper studies whether governments prefer to be leaders or followers in environmental policies. To analyze this question I assume transboundary pollution and two countries that have to decide whether to set environmental taxes sequentially or simultaneously. When taxes are set sequentially an effect, denoted as the sequential setting effect, arises that raises the equilibrium taxes. I show that whether governments prefer to be leaders or followers in taxes depends on the degree to which environmental pollution spills over to trading partners. When this overspill is low enough, taxes are strategic complements and both the leader and the follower obtain greater welfare than under a simultaneous tax setting. However, the leader country obtains greater welfare than the follower. In this case, governments set taxes sequentially. When the degree to which environmental pollution spills over to trading partners is high enough, taxes are strategic substitutes and governments set taxes simultaneously. In this case, each government wants to avoid becoming the follower in taxes.