Cavies (family Caviidae) are a group of rodents distributed over much of South America. The high diversity of habitats inhabited by different species is paralleled by a high diversity of social organizations. Comparisons of behavioral and reproductive strategies between species can provide valuable insights into mammalian social evolution. In this review we 1st summarize the literature to give an idea of the diversity of social and mating systems within the genera Cavia, Galea, Microcavia, and Kerodon. Social systems range from solitary animals through pairs and harems to multimale–multifemale groups. Mating systems of cavies include monogamy and promiscuity and different forms of polygyny. We then review behavioral strategies of females and males that account for this social diversity. Particularly, the role of females and the potential of males to monopolize mates are examined. In some species, for example, estrous females actively solicit copulations with several males and thereby prevent their monopolization by single males. We also discuss adaptations of reproductive physiology to different mating systems. Finally, environmental factors influencing aspects of the social and mating systems of cavies are considered. Particularly, differences in resource distribution, predation risk, and climatic conditions might explain the great variation in species social organization.