Abstract: This paper reports on a comparative study of the external activities of Québec, Scotland, Bavaria, Catalonia, Flanders and the Walloon region. It states that regions are generating an increasing amount of diplomatic activities, both in quantitative and qualitative terms. Furthermore, the article states that currently a third wave is developing in sub-state diplomacy, especially in Europe. This is characterized by steps towards a verticalization of the organisational structure of the department of external/foreign affairs, a strategic re-orientation of the geopolitical and functional priorities and attempts to integrate the external instruments of a sub-state foreign policy into a well performing whole. It is argued that the boundaries between diplomacy (generated by states) and sub-diplomacy are visibly watering down. The following dimensions are studied; (1°) definition of foreign policy, (2°) utilized diplomatic instruments, (3°) organisational structure and operation of the foreign affairs, and (4°) character of the representations abroad. Finally, we try to identify new important research questions for the future in the study of Sub-state Diplomacy