Regions can get involved in international-relations activity defined as paradiplomacy. It is similar to state diplomacy as it is subject to its law and policy and uses similar tools such as diplomatic protocol, but is not pursued by professional diplomats. Regional paradiplomacy needs to be analysed as a source of new international relationships. Consequently, regions should be perceived as new actors in international relations. The article focuses on the paradiplomacy of Polish regions (voivodships, or województwa) and Croatian counties (Hrvatske županije). The case study discusses the cooperation between the Warmińsko-Mazurskie Voivodship and the Split-Dalmatia County.