To unlock multi-vendor HVDC grids and foster the transition of the European energy sector at large scale, InterOPERA proposes a coordinated approach between a diverse, high-level group of industries at the forefront of RES development and grid management. 4 HVDC vendors, 8 TSOs, 2 wind turbine vendors and 3 wind park developers bring their industrial knowledge and practical abilities to make future HVDC systems mutually compatible and interoperable by design, and to improve the grid forming capabilities of offshore and onshore converters. Foreseen and planned HVDC projects will be analysed to define a demonstrator case study. The resulting system-level design will be usable as a guidance to coordinate offshore network planning. This new way of framing the European grid architecture and topology will ensure forward compatibility for future seamless system expansion. Interoperability of control and protection systems will be de-risked through the execution of all necessary activities concurring to the implementation of a real-time physical demonstrator. Concrete results will be delivered through this practical work: detailed functional specifications for each subsystem, standardised models, simulation platforms and interaction study processes, multi-vendor cooperation agreements. Those frameworks will be generalised into operational and strategic tools available to all European stakeholders for the development of multi-terminal HVDC grids that will enhance offshore wind development and integration. Solutions for multi-vendor project procurement, compliant with existing and future regulations, standards and laws, integrating the technical specifications and interoperability assessment tender stages, will be provided to pave the way to the first real-life projects in Europe. External stakeholders will be involved in two-way consultation workshops to maximise the uptake of InterOPERA’s key exploitable results. Recommendations to grid codes and standards will be issued.