Citizen science is currently experiencing a boom in science policy. Citizen participation in the research process is seen as an opportunity to generate socially robust knowledge for sustainable development and as a participatory method for bridging the gap between science and society. This chapter examines the diverse concepts of citizen science and analyses its growing popularity in the context of the digital transformation of science and society. Considering socio-technical developments with regard to human computation, the normative interpretation of citizen science as a more or less desirable democratisation of elitist science falls short of its objectives. The chapter argues instead that the rise of citizen science can also be interpreted as a transitional phenomenon – an intermediate step on the path from individual knowledge acquisition via the crowdsourcing of routine scientific activities to the automation of knowledge production.