The power of placebos to ameliorate symptoms has been with us for centuries. Western medicine today is finding it increasingly difficult to ignore the efficacy of placebos. In some clinical trials with placebos as controls, inert or sham replicas of active pharmaceutical drugs and even sham surgeries have been found to be as beneficial as the intervention being tested. In this volume in the MIT Press Essential Knowledge series, Kathryn Hall examines the power of placebos, showing how their effects can influence our clinical trials, clinical encounters and, collectively, Hall argues, our public health. Hall, who has studied the placebo effect for years, reviews the history of the placebo in medicine, tracing its evolution from quackery and patent medicine to its use as a control in clinical trials. She considers the ways that expectations and learning affect our response to placebos; advances in neuroimaging that reveal the inner workings of the placebo effect; the “nocebo” effect; placebo controls in randomized clinical trials; and the use of psychological profiles and genetics to predict individual placebo response. The effects of placebos have been hiding in plain sight; with this book, Hall helps bring them into clearer view.