When we speak about cooperation normally we mean the capacity to execute joint actions and accomplish jointly established goals. Nonetheless, if more deeply investigated, cooperation is the characteristic of the human beings that has a relevant influence on our mind and intentionality. We do what we do and we are what we are because of the historical cooperative occurrences in which we are embedded. The system of the cognitive skills called mind is what it is because of a cooperative filter that determines what we can do and why we can do it. This book tries to elucidate how the invisible factor of being-withothers determines the cognitive and moral mode of the rational beings.