Colomer states the normative argument at the outset: “[D]emocratic regimes organized in simple institutional frameworks foster the concentration of power … [and] satisfaction of relatively small groups …. In contrast, pluralistic institutions produce multiple winners, inducing multiparty cooperation … and consensual policies that can satisfy large groups’ interests on a great number of issues” (p. 2). The subsequent strategy of the book is as follows. Colomer reviews the fundamental social choice results relating to elections and voting, focusing on the potential for unstable and indeterminate outcomes under simple majority rule. Then he outlines a conceptual framework for the application of theory to the analysis of how real-world political institutions operate and how they develop. The central questions, addressed in sequential chapters, are “Who can vote?;” “How are votes counted?”; and “What is voted for?”

On the first question, Colomer pairs a discussion of the implications of simple versus complex electorates with an historical review of debates over the extension of suffrage. On the second, he outlines the rationales and implications of single-winner versus multiplewinner, and majority versus supermajority decision rules, then illustrates with discussions of electoral systems and rules of legislative procedure in various contexts. On the third, he offers a theory of constitutional design that hinges on whether power is concentrated or divided—either among institutions at the national level (horizontally) or between national and subnational units (vertically). He illustrates with discussions of how authority is distributed in various regimes, and how this distribution either facilitates or impedes the translation of voter preferences into representation and public policy. Each of these chapters is organized around some basic theoretical claims, explained in nontechnical language, then followed with extensive empirical application and discussion. In the conclusion, Colomer provides a brief overview of the establishment of democracies worldwide since the late nineteenth century, arguing that trends in both regime survival and in constitutional design indicate that pluralistic, consensus-encouraging institutions will flourish, while those that encourage concentration of power fade.

The normative case for consensus democracy is familiar from the work of Arend Lijphart, most recently in Patterns of Democracy (1999), and although Colomer's evolutionary argument for its prevalence is suggestive, this is not the central contribution of Political Institutions. The book has a number of strengths. One is the author's knack for supplying historical material that illustrates the relevance of social choice theory to the study of political institutions. In this sense, Colomer's book follows in the tradition of William H. Riker's Liberalism Against Populism (1982), although Political Institutions is empirically richer, and much more accessible to a nontechnical audience.

A second, and related, contribution is Colomer's use of social choice theory to provide an historically and philosophically coherent account of the development of rules for making collective decisions in political institutions, democratic or otherwise. For example, Colomer associates unanimity rules with the premise that decision procedures should aim to discover a single will—for example, divine providence—that governs collective choice. Moves to relax the unanimity requirement, then, are motivated either by a philosophical shift toward identifying the social good with the aggregation of individual preferences, or by the unwillingness to endure the bargaining costs associated with unanimity requirements, or some combination of these. Colomer's account of how rules for electing Roman Catholic popes developed through the Middle Ages is excellent in this regard. His discussions of the development of suffrage and voting rules in medieval European city states, the colonies of the Americas and their successor republics, and nineteenth- and tweentiethcentury European states are similarly absorbing and on point.

No review consisting only of praise can be credible, of course, and so I will offer a few criticisms, purely in the interest of promoting this book. One is that the author's various arguments in favor of consensual institutions amount to arguments for supermajority, or concurrent majority, requirements for decisionmaking. Yet one of the author's points in the initial theoretical primer is that the desirability of more inclusive decision rules depends on how distasteful is the current policy. That is, unless the status quo is universally abhorred, requirements for greater inclusiveness can “allow mediocrity to endure” (p. 73). This point is underplayed throughout much of the book in discussions of the moderating influence of consensual rules on policy outcomes.

A second limitation is the lack of systematic tests of many claims regarding the relationships between rules, policy outputs, and social satisfaction. One example: Colomer posits a chain of reasoning by which the existence of a greater number of elected offices means that fewer policy issues will correspond to each office, such that election results associated with each will be more stable and predictable, thus producing greater social utility (p. 142). Another example: Control by one party over the national government and most subnational governments promotes the centralization of power in the national government (p. 151). These hypotheses, as with many others throughout the book, are derived from basic theoretical principles clearly and plausibly. Nevertheless, they are big claims, to which one can imagine reasonable counterhypotheses. Those who place greater emphasis than Colomer on the costs of bargaining among institutions, for example, would likely be skeptical that there is a straightforward correspondence between the multiplication of offices and the ability of institutions to satisfy their constituents.

Colomer does not elaborate alternative hypotheses nor, for the most part, test his own systematically, relying instead on illustrative empirical examples. He does this so well, however, with such a keen sense for how the basic intuitions from social choice theory map onto real-world politics, that Political Institutions should become a staple of reading lists on positive political theory and comparative politics.