This review sets out four main explanatory paradigms of penal policy— focusing on, in turn, crime, cultural dynamics, economic structures and interests, and institutional differences in the organization of different political economies as the key determinants of penal policy. We argue that these paradigms are best seen as complementary rather than competitive and present a case for integrating them analytically in a comparative political economy framework situated within the longue durée of technology regime change. To illustrate this, we present case studies of one exceptional case—the United States—and of one substantive variable—race. Race has long been thought to be of importance in most of these paradigms and pro- vides a pertinent example of how the different dynamics intersect in practice. We conclude by summarizing the explanatory challenges and research questions that we regard as most urgent for the further development of the field and point to the approaches that will be needed if scholars are to meet these challenges and answer these questions.