Today we know that mirror neurons are not a quirk of a small portion of the premotor cortex but reflect a fundamental functioning mechanism of our brain. In this volume, Rizzolatti and Sinigaglia retrace the studies that in recent years have made it possible to clarify the nature and scope of this mechanism, showing how it is the basis of our ability to understand the actions and emotions of others. It is a particular understanding, which occurs from within, since it rests on the ability to represent and experience those actions or emotions in the first person. In some respects, what we experience when we observe others acting or feeling an emotion is not so different from what we experience when we act or feel an emotion in the first person. And this explains why we are inherently social beings.