The neural mechanisms underlying affiliative behaviors such as pair bonding are best studied in a mammalian rodent, the prairie vole (Mictrotus ochrogaster). Although a large number of avian species are socially monogamous, the neural mechanisms underlying monogamy remain largely unexplored. The experiments presented in the first part of this thesis explore the role of the neurotransmitter dopamine in pair bonding in the socially monogamous avian species, the zebra finch (Taeniopygia guttata). Dopamine is a key player in the mediation of reward in vertebrate species. We hypothesized that pair bonding is a rewarding behavior and therefore would involve this neuromodulator. The dopaminergic pathway consists of dopaminergic neurons that project from the ventral tegmental area (VTA) that project into the medial striatum. We measured levels of dopamine in the medial striatum and activity of dopaminergic neurons in the ventral tegmental area (VTA) in unpaired and paired zebra finches. Additionally, we observed the effects of dopaminergic antagonists on pairing behaviors. The activity of VTA dopaminergic neurons and dopamine levels in the medial striatum were higher in paired versus unpaired birds but blocking dopaminergic neurotransmission via two receptor subtypes did not prevent the formation of pairs in this species. The second major theme in this dissertation has been to explore the role of early social environment and its role on the development of the stress response as well the development of mate choice and pairing behaviors in adulthood. Zebra finches were raised solely by their fathers (female-deprived) in the absence of their mothers. When these offspring reached adulthood, they were subjected to stressors such as isolation and restraint. We found that female-deprived adults were hyperresponsive to isolation as compared to control birds that were raised with both parents. Additionally, corticosterone receptor levels were altered in femaledeprived offspring. Finally, a significantly higher percentage of female-deprived offspring formed pairs with other female-deprived males. These results suggest that early life perturbation of the social environment affects mate choice as well as stress physiology of offspring in adulthood.