AbstractThe most important factor that defines citizen science is that non-professional scientists contribute to scientific research. Therefore, it is important to recognise the perspectives and experiences of these participants. Projects may provide ways for participants to contribute to scientific research at different stages of the scientific process according to different levels of engagement. Understanding what motivates citizen scientists to engage in a project, and subsequently matching the project to these motivations, will help project leaders to recruit and retain participants. In addition, it is important to understand what benefits participants gain from engagement in citizen science projects. For individual projects, this will help ensure that scientists as well as participants benefit. For the wider field of citizen science, this will provide evidence of the potential impact of citizen science on participants. However, participants may also encounter challenges during their engagement with citizen science projects. Project leaders and scientists should plan in advance to address these challenges and ensure that relevant expertise is present in the project team.