Subnational diplomacy has become an increasingly important part of foreign policy and international relations. This observation concerns a state of affairs that is not necessarily obvious or given. First, by definition, subnational governments usually conduct subnational activities and address problems that affect their constituencies. Second, in many countries subnational governments undertake such an agenda without an actual legal framework authorizing such initiatives. However, with an intensified global interdependency, policy areas such as environmental protection, human rights, immigration, and trade, just to name a few, require action both at the international and territorialized levels, as many of them transcend political administrative boundaries. As a result, in the early 21st century it is possible to determine various forms of international relations conducted by subnational leaders. This activity involves direct interactions undertaken by subnational leaders and bureaucrats with other actors across borders (private, non-governmental, and governmental—national or subnational), participation in transnational networks, and/or participation in international policymaking. Because subnational governments are closer to the people and can test experimental or groundbreaking policies with less risk, oftentimes they can become pioneers of measures that can be rolled out or replicated elsewhere in the international domain. Such policy leadership is just one element of subnational engagement in the diplomatic arena whereby subnational governments move across jurisdictional levels, breaking the fixed scales in which they would traditionally operate. In the past years, scholars investigating the external relations undertaken by subnational governments have dedicated great effort to understanding the motivations for regions to go into the international arena. What these studies lack, however, is an understanding of what the implications are of subnational governments’ engagement in international relations.