The hydrogen valley will build an integrated Baltic Sea hydrogen economy to boost energy security and cut emissions. A hydrogen valley is a regional system where hydrogen is produced, distributed, and used across different sectors in an integrated way. One of the most ambitious projects of this kind is BalticSeaH2, which is creating the first large-scale cross-border hydrogen valley between Southern Finland and Estonia. The hydrogen valley is designed to serve as a model for regional cooperation across borders and to demonstrate how hydrogen value chains can be scaled up in practice. By demonstrating how a hydrogen valley can be developed across borders, it provides valuable lessons for other regions in Europe.