This paper presents the foundations of a systematic epistemic case for democracy as a collective decision-rule and explores the implications of this epistemic claim for normative justifications of democracy, scientific explanations of its empirical success, and policy reforms. As far as the epistemic case is concerned, the paper proposes an account based on the concept of “democratic reason,” or the collective intelligence of the people in politics. The paper argues that, counter-intuitively, democratic reason is more a function of the cognitive diversity of the individuals taking part in the decision than of their individual ability. As an account of democracy’s epistemic benefits, the argument from democratic reason supplements procedural accounts based on fairness and equality to provide a complete functionalist explanation of democracy. Finally, the argument supports policy reforms increasing citizens’ participation in the collective decision-process.