In this paper, I dispute what I call psychological internalism about moral responsibility, which comprises most classic accounts as well as newer neurobiological ones, and I defend psychological externalism about moral responsibility instead. According to psychological internalism, an agent's moral responsibility is determined solely or primarily by her intentional states. I argue that psychological internalism is empirically challenged by recent findings in social psychology and cognitive science. In light of the empirical evidence, I contend that moral responsibility depends on historical and environmental factors to a much greater degree than previously appreciated. Thus, moral responsibility is not just in the head: indeed, it is much less in the head than typically assumed.