Global restructuring has dramatically affected the value, extent, and significance of informal economic activities worldwide. Approaching informalization as a systemic phenomenon, this essay illuminates linkages among economic processes, widening inequalities, “governance gaps,” and global insecurities. It considers the historical context in which distinctive approaches to informality emerged and reviews three principal “islands” of existing research: mainstream, structuralist, and feminist. These variously illuminate patterns of economic inequality that are central to studies of international political economy. Informality’s significance to IR and security studies is further illuminated through a discussion of the processes and political economy of informalization in relation to global migrations, and the interaction of economic and political informalization in the context of “new” wars and security crises.