Prep4Blue, as a Coordination and Support Action (CSA), contributed to setting the foundation for the successful implementation of the EU Mission “Restore our Ocean and Waters by 2030.” A central focus of the project was to support public mobilization— one of the Mission’s enablers—by developing strategies, tools, and activities to engage both citizens and stakeholders in Mission-relevant research and innovation. To address this goal, Prep4Blue established two dedicated work packages: WP3 focused on citizens, defined as non-specialist individuals acting outside formal organizational structures. WP6 addressed stakeholders, understood as organised actors such as public authorities, businesses, researchers, NGOs, and civil society. Prep4Blue’s activities supported both groups through: The development of stakeholder engagement guidelines and a dedicated online tool (WaveLinks) to help future Mission projects choose suitable engagement methods. The launch of a Mission engagement Helpdesk, along with a series of stakeholder and citizenfocused webinars to support knowledge sharing and capacity building. Engaged research with citizen networks, and training workshops focused on ocean literacy, behaviour change, and inclusive participation. The organisation of pilot stakeholder assemblies and the creation of a Community of Practice, which brought together actors from across Europe to test participatory and collaborative approaches in support of Mission objectives. Despite this methodological approach, throughout its lifetime, Prep4Blue recognised the fluidity between citizens and stakeholders, while maintaining separate engagement strategies tailored to the needs of each. The tools, resources, and lessons generated by the project are now available for use by Horizon Europe projects and other Mission-aligned initiatives, helping to ensure that public engagement is inclusive, meaningful, and aligned with the 2030 goals of the Mission. Please note that this deliverable has not yet been accepted by the funding authority. As such it may be subject to change.