The Calculus of Consent: Logical Foundations of Constitutional Democracy is a groundbreaking work in democratic theory. This chapter argues that it is of continued relevance today, due both to its methodological innovations and its use of those innovative techniques to solve the fundamental problem of democratic justification. In Calculus, James Buchanan and Gordon Tullock fuse economic methods, political theory, and the normative project of showing how democratic institutions of a particular sort can be justified contractually, creating a unique form of democratic contractualism that came to be known as “Constitutional Political Economy” and the more general research program of “Public Choice Theory.” Although these pioneering techniques have been integrated into mainstream political theory, the interest of their normative project has not been similarly appreciated.