I identify 4 topics for future research. 1) Our knowledge of rodents from the developing world is limited, yet recent evidence suggests that many species are highly social. I concentrate on South American rodents to demonstrate the wealth of information available when we study these taxa and incorporate the findings into our current paradigms of social evolution. 2) Relatively little is known about proximate mechanisms that govern social systems. Research on the neuroendocrine basis of pair-bond formation and paternal care has provided valuable insights, but many questions remain. 3) Mounting evidence indicates that, in addition to genetics, social environment can play a major role in behavioral and physiological development. Studies on effects of early social environment would contribute to our understanding of ontogeny of individual differences in social species. 4) Recent evidence suggests a significant geographic variation in social characteristics of some rodent species. The extent and ecological correlates of such intraspecific variation merit further investigation.