A neurobiological model for pair-bond formation has emerged from studies in monogamous rodents. The neuropeptides oxytocin and vasopressin contribute to the processing of social cues necessary for individual recognition. Mesolimbic dopamine is involved in reinforcement and reward learning. Concurrent activation of neuropeptide and dopamine receptors in the reward centers of the brain during mating results in a conditioned partner preference, observed as a pair bond. Differential regulation of neuropeptide receptor expression may explain species differences in the ability to form pair bonds. These and other studies discussed here have intriguing implications for the neurobiology of social attachment in our own species.