Individual and household actions now directly cause approximately 38% of total national carbon dioxide emissions, and that percentage has increased in recent years. These emissions can be reduced by almost 30% with existing technology, but this potential remains unrealized even though people are motivated to reduce their emissions and the economics are favorable. This paper argues that the potential remains largely untapped in part, because of a shortage of clear, coherent, credible, and actionable advice concerning which individual and household actions are most effective. It develops a prioritized list for the United States, based on national averages, of the most effective household-level actions for reducing carbon dioxide emissions. Available evidence indicates that people have often been mistaken about where the greatest opportunities for reduction lie. Conflicting and confusing messages and the difficulty of getting accurate information may be serious barriers to effective change. We conclude that more policy attention needs to be devoted to reducing individual and household contributions to climate change, beginning with developing accurate and credible information that individuals can use to prioritize behavioral changes.