Over the last ten years or so, it has become commonplace to hear talk of an obscurantist threat linked to a rise in irrationality, manifested mainly by a mistrust of vaccination and conventional medicine. But obscurantism can also be found where we pride ourselves on fighting it. In this case, it is no longer the work of marginal or anti-establishment groups, but of a dominant way of thinking that presents itself as that of science and rationality. The aim of this book is to lift the veil on this obscurantism in power. Through numerous examples, from impeded research into unexplained phenomena such as near-death experiences, to the vast field of medicine where the pharmaceutical industry has cornered the market on proving the usefulness of a treatment, Brice Perrier reveals how reason is transformed into dogmatism and hinders the advancement of knowledge. The aim of the book is not to say what is true or false, nor to settle scientific controversies, but to understand why these debates, which have always been legitimate and even necessary in science, may simply no longer be allowed.