During the heyday of sociobiology in the 1960s, 1970s, and 1980s the question of altruism rose to the forefront of evolutionary thinking and stirred up considerable debate. Indeed, it would be difficult to overestimate the theoretical importance of altruism in sociobiological accounts of behavior. Altruism appears to be deeply problematic from certain evolutionary perspectives because, by definition, it implies that an individual engages in behavior that benefits others at one’s own expense and thus would be selected against. So the essential dilemma is this: how could truly altruistic behavior evolve in the egoistic universe envisioned by Darwin’s theory? In this chapter we shall answer this question in three complementary ways. Apparently altruistic behavior could evolve if it turns out that it ultimately benefits the individual in terms of (1) inclusive fitness, or (2) delayed benefits resulting from reciprocity. Finally, altruism could also evolve if it ultimately benefits the group. This third mechanism is only possible if natural selection of competing groups trumps selection pressures operating against altruism within the group. We first examine mechanisms that enable cooperation within the selfish gene paradigm emphasizing the gene’s level of selection.