The present research examined links between attachment to pets and psychological well-being in different populations. Key factors among pet owners that were expected to moderate the relationship between attachment and well-being, notably social connectedness and genetic polymorphisms relating to oxytocinergic functioning, were also explored. Survey responses and saliva samples were gathered from attendees at a pet exhibition (Study 1), members of the public (pet owners and non-owners) at a mall and museum (Study 2), and low-income, marginally housed pet owners (Study 3). Pet owners reported greater quality of life and were more likely to have a polymorphism of the oxytocin receptor gene (rs225429). However, across all three studies, greater attachment to pets was associated with negative psychological well-being and the presence of physical health conditions. Overall, findings suggest that pet attachment and its relation to human well-being can differ depending on psychosocial characteristics of pet owners.