STRING is a political cross-border organisation spanning five cities (the Free and Hanseatic City of Hamburg, Copenhagen, Malmö, Gothenburg and Oslo) and eight regions (Schleswig-Holstein, Region of Southern Denmark, Region Zealand, Capital Region of Denmark, Region Skåne, Region Halland, Västra Götalandsregionen and Viken County) across Germany, Denmark, Sweden and Norway. Home to around 14 million inhabitants, STRING has good potential to become a leading European megaregion and an internationally acknowledged Green Hub if governments “think big” and work together beyond their own boundaries. Building on its green expertise and high levels of innovation and quality of life, STRING could take advantage of current opportunities such as the construction of the Fehmarn Belt Fixed Link to reap the benefits of agglomeration economies and establish itself as a sustainable megaregion. However, time is of the essence. Seizing the political momentum of the coming decade, including the momentum to support a green recovery from COVID-19, will be critical to advance STRING’s green vision and shape a future-proof economic model.