Abstract: A constitutional order is a system of systems. It is an aggregate of interacting institutions, which are themselves aggregates of interacting individuals. In The System of the Constitution, Adrian Vermeule analyzes constitutionalism through the lens of systems theory, originally developed in biology, computer science, political science and other disciplines. Systems theory illuminates both the structural constitution and constitutional judging, and reveals that standard views and claims about constitutional theory commit fallacies of aggregation and are thus invalid. By contrast, Vermeule explains and illustrates an approach to constitutionalism that considers the systemic interactions of legal and political institutions and of the individuals who act within them.