The Clean Energy Transition Partnership (CETP) is a transnational initiative on joint RTDI programming to boost and accelerate the energy transition, building upon regional and national RTDI funding programmes. It aims to empower the energy transition and contribute to the EU’s goal of becoming the first climate-neutral continent by 2050, by pooling national and regional RDTI funding for a broad variety of technologies and system solutions required to make the transition. It will foster transnational innovation ecosystems from the very local and regional level, up to the transnational European level, thus overcoming a fragmented European landscape. The CETP is aiming to enable 70 national and regional RDTI programme owners and managers from 32 countries to align their priorities and implement annual joint calls from 2022 to 2027 (original first proposal as published by the EC on CORDIS). Actually 30 countries and 55 programme owners and managers formally participate in this Initial Grant Agreement. They also organise joint accompanying activities to enable a dynamic learning process, extract strategic knowledge (“Knowledge Community”) and maximise the impact (“Impact Network”) to accelerate the upscaling, replication and market diffusion of innovative solutions. This will foster the uptake of cost-effective clean energy technologies. The common vision of the CETP is already manifested in its Strategic Research and Innovation Agenda (SRIA) that has been co-created in a broad engagement process during 2020, together with the involved countries, the EU SET-Plan Implementation Working Groups and ETIPs, all energy relevant ERA-Nets as well as the EERA joint programmes (over 500 editors, co-authors, commenters and discussants). The SRIA was endorsed together with the European Commission (DG RTD and ENER) in November 2020. This articulates the common goal of (1) building a transnational transformative Joint Programming Platform, (2) developing and demonstrating technology and solutions for the transition of energy systems, and finally (3) building innovation ecosystems that support capacity building at all levels.