Oxytocin is a neuropeptide that has been implicated in a range of social behaviors, such as attachment, trust, and empathy. Additionally, it has been suggested that through its promotion of prosocial behaviors, oxytocin might contribute to mental health outcomes. Chapter 1 described research indicating that oxytocin interacts with several neuroendocrine, neurotransmitter, and inflammatory processes that are linked to depressive disorders. Moreover, it was suggested that oxytocin might not always be beneficial, but instead serves to increase the salience of social cues, such that positive or negative experiences result in greater responses, thereby influencing affective states. In Study 1 (N=225), unsupportive social interactions were related to higher depressive symptoms through greater emotion- and lower problem-focused coping, but these relations were stronger among individuals that carried a single nucleotide polymorphism (SNP) on the oxytocin receptor gene (OXTR). In essence, individuals with a genetic variant thought to be linked to lower oxytocin endorsed potentially less advantageous coping methods. Study 2 (N=476) similarly revealed that unsupportive relations were associated with negative affective states, and this association was stronger among those with the OXTR SNP, as well as those with an oxytocin-related genetic variant on a gene involved in the regulation of oxytocin release (CD38). Study 3 (N=128) revealed that these genetic variants were related to altered reactions to experimentally manipulated social ostracism. In contrast to the previous studies that linked lower oxytocin functioning to negative outcomes, in the context of social ostracism, individuals with the OXTR allele thought to be tied to greater oxytocin functioning, were more psychosocially and physiologically reactive to social rejection. This finding is consistent with a social sensitivity perspective of oxytocin. A social sensitivity effect was not as apparent when examining relations between the CD38 gene and responses to ostracism. Finally, Study 4 (N=67) revealed that endogenous levels of oxytocin were related to coping strategies in response to a psychosocial stressor, and the strategies endorsed varied as a function of whether individuals had support present or not. These findings highlight the potential influence of oxytocin on stress-related coping processes, which could in turn affect vulnerability to mood outcomes.