How does our brain make us feel what others feel? How does it motivate us to help others? We will start by showing that while witnessing the actions of others, we not only recruit regions involved in our own actions, but these regions feed-back predictions of upcoming actions back to parietal and sensory regions, creating a predictive social brain. Thereafter concentrating on emotions, we will start from the observation that in humans, the somatosensory, insular and cingulate cortices are activated both when experiencing pain and while witnessing other do so. Through a series of human and rodent examples we will then ask whether such vicarious activations have causal influences on sharing the emotions of others and on deciding to help them. We will leverage invasive methods to show that signals in the human insula indeed quantitatively represent the pain of others, and that in the rodent cingulate cortex, neurons responding to the animal’s own pain become reactivated when witnessing the pain of others. In the light of these findings in rodents and humans, and the homologies in their brain circuitry, we will suggest that emotion sharing is an evolutionarily conserved mechanism that allows animals and humans to better prepare for yet unseen dangers by tuning into the state of those that have already detected them. Finally, we will present work on psychopathic criminals and healthy volunteers that highlights that although these circuits may be biologically pre-wired, we have control on how much we use them. Empathy does not just happen to us: we can choose to empathize.