The reactions that science triggers on the people it studies, describes, or theorises about, can affect the science itself and its claims to knowledge. This phenomenon, which we call reactivity, has been discussed in many different areas of the social sciences and the philosophy of science, falling under different rubrics such as the Hawthorne effect, self-fulfilling prophecies, the looping effects of human kinds, the performativity of models, observer effects, experimenter effects and experimenter demand effects. In this paper we review state-of-the-art (...) research that falls under the remit of the philosophy of reactivity by considering ontological, epistemic and moral issues that reactivity raises. Along the way, we devote special attention to articles belonging to this journal's Topical Collection entitled “Reactivity in the Human Sciences”. (shrink)