Twinning to Sustainable Energy Transition (hereinafter TWINN2SE) is implemented as a partnership between the Greek Institute of Geoenergy of the Foundation for Research & Technology – Hellas (FORTH/IG), the Norwegian University of Stavanger (UiS)  and the French Research Center IFP Energies Nouvelles (IFPEN), in the domains of 1) Carbon Capture and Storage (CCS), 2) Deep Geothermal Energy and 3) Subsurface Hydrogen Storage. The project consists of a capacity building & mentoring programme in the above three areas which will be complemented by an exploratory project focusing on Hydrogen storage in Geological formations, fostering interdisciplinary competencies at the interplay of a promising energy vector with subsurface reservoir characterisation, modelling and monitoring.