Abstract: Misperceptions of others’ concern about climate change have been identified as key barriers to climate action. We study whether people also misperceive (i) others’ level of sustainable behavior, (ii) the level of sustainable behavior others deem appropriate, and (iii) others’ support for policies that restrict or tax individual nonsustainable behavior. We address these questions in a pre-registered online study with 1,292 Luxembourg residents. Participants reported their own behaviors, personal norms, and policy support, and estimated the same for others across three domains with high carbon-saving potential: reducing animal protein consumption, reducing home heating, and using public transportation. In line with pluralistic ignorance, we find that a majority of participants systematically and substantially underestimate others’ sustainability. Participants also underestimate how much others donate to offset carbon emissions in an incentivized donation task. Consistent with a false consensus effect, the least sustainable individuals strongly underestimate others’ sustainability, while the most sustainable underestimate less and even overestimate in some domains.