This book is an introduction to the logic and analytics of group choice. To understand how political institutions work, it is important to isolate what citizens - as individuals and as members of society - actually want. This book develops a means of ‘representing’ the preferences of citizens so that institutions can be studied more carefully. This is the first book to integrate the classical problem of constitutions with modern spatial theory, connecting Aristotle and Montesquieu with Arrow and Buchanan.