An increasing amount of citizen science projects involve citizens on levels of participation that go beyond data collection and entail the co-creation of research questions and methods, as well as the project pathway. The success of such projects depends on the establishment of shared knowledge, a task that can be especially challenging in citizen science that focuses on complex societal issues and the so-called wicked problems. We suggest that this challenge can be addressed through a deeper engagement with research on mental models -- cognitive representations of external reality that largely define human thinking, decision-making and behaviour. Moreover, particular emphasis should be put on the effective co-creation of shared mental models, whereby design thinking could provide valuable methodologies and tools. The objective of the workshop “Mental Models in Citizen Science” was to dive into mental model theory and design thinking toolbox, and to explore their potential for citizen science. This paper provides an overview of the workshop activities and insights, and proposes a research agenda shaped around mental models and their role in citizen science.