Citizen science refers to individuals without formal scientific credentials involved in knowledge production activities. Citizen scientists most commonly take on data collection, especially environmental monitoring of various sorts; they may also become involved in coordinated online efforts to interpret images and other data sets. One kind of activity that the term citizen science is often used to describe takes place among communities who are both experiencing some negative impact and unsatisfied by official responses, which may deny the existence of a problem. The term citizen science encompasses two distinct traditions of participation by non-scientists in scientific knowledge production: one critiques the universalizing, values-denying model of science that is currently institutionalized in academic and policy spheres; the other strives to extend its authority to scientist-led research projects that incorporate efforts of uncredentialed individuals. Despite their limitations, the frameworks for citizen science developed in the scientific authority-driven tradition have come to dominate both academic conversation and governments' efforts to institutionalize citizen science.