Mirror neurons are a set of neurons that discharge both when the monkey executes a specific motor act and when it observes another individual doing a similar act. In the first part of my talk, I will review the basic functional properties of monkey frontal mirror neurons. I will describe first their motor properties showing that they code the goal of a motor act. I will review then their visual properties and present evidence that mirror neurons represent a mechanism that allows a direct understanding of what the agent is doing. Mirror mechanism also exists in humans. I will present the data proving it will show evidence that, although there are other mechanisms through which one can understand the behavior of others, the mirror mechanism is the only one that allows understanding others “from the inside” providing the observer with a “first-person” person grasp of others’ motor goals, intentions and emotions. I will conclude discussing the relationship between autism deficits and damage to the mirror mechanism. I will show that while children with autism understand the what of an observed motor act, they fail to recognize the why behind it. Because of these impairments, children with autism lack experiential understanding of others and rely on external factors in their behavior.