Now that citizen science in the health domain is becoming more established, it is relevant to scale it up to tackle larger projects. Several things can be done such as the definition and introduction of liability and oversight models that would be the analogue of the traditional IRB (institutional review board), and the professionalization of participant roles in the study ecosystem such as that of the study manager.A more subtle issue is to develop an epistemology of citizen science. This would provide a structure and context for exploring the knowledge that is derived from citizen science. One question is whether new kinds of knowledge are being formed through group collaborations such as wikipedia and health social networks. Another question is characterizing the differences (if any) in the types of knowledge generated by traditional medicine, self-experimentation, and health collaboration communities.