It is widely recognized that communications that make social norms salient can be effective in influencing behavior. What is surprising, given the strength of the evidence, is how little people are aware of the extent to which social norms affect their own behavior. Consequently, this low-cost persuasion strategy is considerably underutilized to promote behaviors to help reduce climate change. In this paper we review recent field experiments that harness the power of social norms to influence pro-environmental behavior. We also elucidate the circumstances under which providing normative information is optimal, as well as circumstances under which such information can backfire to produce the opposite of what a communicator intends.