The dissertation explores the role of scientific rationality and religious reasoning in democratic law and policymaking. How does legitimate law and policymaking proceed in light of disagreements on science and religion? This question is addressed within the framework of public reason. Roughly public reason is the idea that coercive state power must be justifiable to those subject to it. The public reason idea and ideal has a long tradition in political philosophy and legal scholarship, but it is also found in our actual political and judicial practices. When addressing the science and religion question within the framework of public reason, questions like the following arise: Can binding laws and policies be justified with the use of religious reasons? Must public officials who propose and decide on binding laws deliberate in accordance with established science? Does the question concerning the role science and religion in political deliberation challenge the public reason framework as viable vehicle for pursuing democratic legitimacy? The dissertation discusses these and other questions related to the special role of science and religion in liberal democracy.