In this chapter, we introduce our theoretical framework, which delineates alternative answers to the research question concerning the conditions under which peaceful borders might enable the occurrence and proliferation of illicit transnational flows. To answer this question, we assume that international peace and globalization act as permissive conditions that provide the general context for the occurrence and proliferation of illicit transnational flows across peaceful borders as parameters. At the same time, we explain the variation in the nature, occurrence, quality, and quantity of these illicit transnational flows according to three variables: (1) the degree of physical and institutional openness of the peaceful borders; (2) the degree of governance, institutional strength, and political willingness of the neighboring states; and (3) the prevalent socioeconomic conditions of the neighboring states, with reference to the regional economic characteristics of the borderlands. In addition, we discuss the methodology and introduce the case studies that illustrate and test the theoretical argument.