In the awarded paper, the authors Julia Suess-Reyes, Susanne Beck, Robin Brehm, Marion Poetz from the OIS Center, together with Henry Sauermann propose a novel conceptualization of engaging citizens in scientific research projects. In a first step, the authors suggest “Participation in Decision Making” as a key defining feature of deep crowd engagement and co-created projects, as this allows citizens to truly shape the direction of the entire project. In a second step, the authors analyze 23 interviews with citizens and professional scientists from ten co-created citizen science projects in Europe and the USA to surface challenges that are particularly relevant to joint decision-making. The paper further outlines meaningful practical implications for everyone engaged in realizing citizen science projects.