American democracy is at risk. Fueled by partisan news and emotion-stoking social media, Americans are becoming less and less able to think rationally about the challenges facing the country. For self- governance to succeed, citizens must analyze issues objectively, engage with one another respectfully, and ground their disagreements in reason and facts. At this precarious moment in our history, we need a renaissance in critical thinking. And it can start in the math classroom. Composed as a letter to fellow educators, Dear Citizen Math offers an inspiring new vision for math class: as a forum for discussing the most important and interesting issues in society, from healthcare reform to global pandemics, fake discounts to the acceleration of technology. For generations students have viewed mathematics as a set of random skills to memorize and concepts with a little connection to reality. In fact, math is a powerful prism for exploring and making sense of the world, and math teachers can be the most influential leaders in American democracy. They have the potential to kindle a newfound commitment to reason and cultivate a more thoughtful citizenry.