The subject of the chapter is the change in horizontal intergovernmental relations in Greece—with emphasis on the impact of the recently induced EU strategies. The main question examined is whether there are advancements in horizontal intergovernmental cooperation in Greece capable of improving the country’s position in the EU Multilevel governance (MLG) which serves the “Green” and “Digital” strategy. We begin by briefly presenting and discussing the government system of Greece as well as its horizontal and vertical dimensions—all embedded in an EU MLG system. The size, potential and “centrality” of municipalities are specifically important for understanding intergovernmental coordination in Greece. We examine the types of collaborations between municipalities and regions and try to clarify the strong points and weaknesses of these collaborations through appropriate examples. Then, we discuss the pressures for change on the Greek horizontal intergovernmental cooperations: from the effects of the Greek fiscal crisis to the influence of the new EU strategies and the most recent developments: COVID-19, energy/Ukraine and so on. Finally, we present relevant conclusions and appropriate policy proposals for improvements in the horizontal intergovernmental cooperation in Greece.