Buchanan and Tullock’s seminal work, The Calculus of Consent, linked economic methodology to substantive questions in political science. Among the major contributions of the book is a connection between constitutional decision making and contractarianism, a philosophical tradition that proponents believe can give institutions legitimacy. In other words, a major contribution of their book is a clear connection between empirical decision making and normative principles. This book formalizes and extends this foundational work as it attempts to show how economic and philosophical arguments about the "best" voting rules can be used to improve constitutional design. It informs debates about constitutional political economy in comparative politics, democratic theory, and public choice. Political scientists often ask questions about what causes a nation to seek a new constitution, how constitutions are made, and what factors allow for corruption in constitutional decision making. The Calculus of Consent and Constitutional Design bridges the gap between normative questions about which institutions are most efficient and fair and empirical questions about how constitutions are formed. This provides a benchmark to help create better constitutions and informs empirical research about what institutions are most likely to succeed. The book begins by showing how contractarian ideals can be used to justify choices about decision-making. It then carefully defines several concepts employed by Buchanan and Tullock and shows why the relationships between these concepts may not be as closely linked as Buchanan and Tullock first thought. This provides a backdrop for analyzing the three phases of constitutional decision-making: 1) the constitutional phase, where rules for constitutional decision making must be justified; 2) the legislative phase, where the optimal k-majority rule1 is analyzed; and 3) the electoral phase, where the optimal voting rule for large electorates and open alternatives are determined. These phases differ by context and sources of legitimacy. Computational models and analytic techniques are introduced in each of these chapters. Finally, the book concludes with statements about the significance of the research for the creation of constitutions more broadly.