The aim of the EU-Citizen.Science project is to build a sustainable platform as a mutual learning space for citizen science in Europe through an inclusive and transparent approach. To achieve this aim, the project supports the development of a framework to identify, collect and share good quality citizen science resources and best practices. This deliverable (D3.1) "Framework report describing criteria and rationale for sharing and selecting state of the art citizen science resources" describes the set of criteria and actions for identifying good quality citizen science resources for the EU-Citizen.Science platform. It also explains the methodology of the criteria development process along with the challenges faced throughout. Finally, the report elaborates on the implementation of the criteria before and after the launch of the platform.