Science Europe, cOAlition S, OPERAS, and the French National Research Agency (ANR) present an Action Plan for Diamond Open Access to further develop and expand a sustainable, community-driven Diamond OA scholarly communication ecosystem. It focuses on efficiency, quality standards, capacity building, and sustainability, and it addresses the alignment and development of common resources for the whole Diamond OA ecosystem, including journals and platforms, while respecting the cultural, multilingual, and disciplinary diversity that constitutes the strength of the sector. The Action Plan intends to create an inclusive worldwide community that has the tools to strengthen existing Diamond OA journals and platforms and increase their visibility.