Citizen Science (CS) is related to public engagement in scientific research. The tasks in which the citizens can be involved are diverse and can range from data collection and tagging images to participation in the planning and research design. However, little is known about the involvement degree of the citizens to CS projects, and the contribution of those projects to the advancement of knowledge (e.g. scientific outcomes). This study aims to gain a better understanding by analysing the SciStarter database. A total of 2,346 CS projects were identified, mainly from Ecology and Environmental Sciences. Of these projects, 91% show low participation of the citizens (Level 1 ‘citizens as sensors’ and 2 ‘citizens as interpreters’, from Haklay’s scale). In terms of scientific output, 918 papers indexed in the Web of Science (WoS) were identified. The most prolific projects were found to have lower levels of citizen involvement, specifically at Levels 1 and 2.