The EU-Citizen.Science Engagement and Community-building Plan is Deliverable 2.2 (D2.2) from the coordination and support action (CSA) EU-Citizen.Science, grant agreement (GA) 824580. It outlines how the project will ensure that target stakeholders engage actively and sustainably with the EU-Citizen.Science platform, both during the project period (2019-21) and beyond. It provides an overview of key target audience identified, and their prioritization, a deep understanding of needs and expectations of the target audience which has been selected as a starting point for the community engagement process, as well as suggestions for a series of actions that the project will implement to meet those expectations and therefore stimulate community engagement. The main objectives of this deliverable are to: Explain the process leading to the identification of a key target audience group; Outline how the understanding of their needs and expectations has been achieved, through a research approach based on semi-structured interviews; Suggest concrete actions to address those needs and expectations, as well as keep this key community engaged in the preparatory phase and launch of the Platform; Plan future steps, in view of making the engagement and community-building plan an iterative process that starts with the publication of this deliverable, and evolves throughout the project, focusing on understanding and engaging all key target audience identified.