BalticSeaH2 will establish the first, largescale interregional hydrogen valley in Europe. BalticSeaH2 will build a main cross-border Hydrogen Valley between Finland and Estonia and connects it with local valleys in different countries surrounding the Baltic Sea. The ultimate goal is to develop an international hydrogen economy and markets that work optimally both from the technical, economic and environmental perspectives across country borders in the Northern Europe, more specifically around the Baltic Sea. The project will develop, scale and demonstrate hydrogen use in production, storage and distribution, and in Use Cases in different sectors from industry, mobility and energy. The learnings from the cross-border build-up of a hydrogen economy will be shared with specifically identified Connected Valleys and replicated across borders between them, but furthermore, shared to boost replication and initiate new hydrogen valleys across Europe. The cross border Main Valley is to be located in the region of Southern Finland – Estonia. These regions are already connected with a natural gas pipeline, transmission cable and maritime operations and the Transmission System Operators (TSO) in both countries collaborate actively in the further development of the cross border infrastructures. The cross border nature of the Main Valley makes is possible to develop cross border markets and businesses for green hydrogen production, transport and use from the start, including also development of cross border neighbouring pricing zones for renewable electricity to reach optimized system, market and business designs for an efficient hydrogen economy.