Studying social behavior in animals can help us identify the causal neural mechanisms of the trait dimensions that combine to promote individual differences in social behavior with relevance for human mental health. Social behavior is a broad term that encompasses numerous brain and behavioral systems. In this chapter, we focus on the nonhuman animal literature concerning neurobehavioral systems thought to underlie affiliative capacity. We define affiliative capacity as a component of social behavior associated with the potential to focus on and engage with social stimuli to derive broad health benefits from prosocial interactions. We highlight commonly used behavioral tasks and genetic methods in non-human animal social neuroscience research for evaluating individual differences in affiliative capacity. Next, we describe an illustrative animal model example of individual differences in a phenotype at the neural level contributing to individual differences in affiliative behavior. We also describe evidence from animal models for experience-dependent development that may contribute to individual differences in affiliative capacity across the lifespan. Insights from social neuroscience research in non-human animals can inform our understanding of human mental health as we consider the limitations of our current understanding and develop future directions.