This complex, ambitious, and large book seeks to question, reformulate, and enhance the scope (and methods) of inter- national relations theories, particularly those formulated within a realist framework. The authors question that frame- work, the Westphalian model of putatively unitary nation- states, quantitative methods of empirical investigation, and the levels-of-analysis paradigm. The breadth of their critique is extensive and, consequently, highly ambitious. Rather than approach international relations as a system of unitary nation-states inspired by realist principles, which is arguably a partial and simplified portrayal of contemporary research, the authors favor a complex system of "overlapping, layered, and linked polities" that have both horizontal and vertical dimensions. The latter dimension is particularly important, as it concerns patterns of authority, identity (including ethnic- ity), and institutions that compete for the loyalty of individ- uals.