The European Citizen Science Association (ECSA) is a non-profit association set up to encourage the growth of the Citizen Science movement in Europe. It draws on 200 individual and organizational members from over 28 countries across the European Union and beyond. Launched during the EU GREEN WEEK in June 2013, ECSA has grown from an informal network of researchers and communicators interested in Citizen Science into the European reference network of Citizen Science initiatives. ECSA builds on the substantial expertise of its members in order to mobilize Citizen Science as means for evidence-based sustainable development. As spelled out in our strategy, ECSA will conduct research and support refinement of methodologies, increase capacities and develop three interrelated key competencies: - Promoting Sustainability through Citizen Science, - Building a Think Tank for Citizen Science, - Developing Participatory Methods for Cooperation, Empowerment and Impact.