Although Latinos are the largest minority group in the country, research examining how different psychological and cultural variables affect Latino individuals' wellbeing is disproportionately developed and cross-cultural comparison studies are particularly scarce. To address these issues, this dissertation research examined cross-cultural adult attachment-social self-efficacy-psychosocial wellbeing conceptual mediational model while investigating the moderator effects of country membership and familismo on the proposed mediational model using a cross-cultural sample of Mexican and Mexican-American university students. A total of 595 participants, including 360 Mexican students from Mexico and 235 Mexican-American students from the United States completed the research questionnaires. Results indicated that social self-efficacy was a significant mediator for the effects of insecure attachment on life satisfaction and conflict resolution in both cultural groups and for the links between attachment insecurity and depressive symptoms in the Mexican-American group. Additionally, moderated mediation analyses showed that country membership was a significant moderator for the links between attachment avoidance and social self-efficacy when life satisfaction, conflict resolution style, and depressive symptoms were the dependent variables, as well as for the direct link between attachment anxiety and physical health symptoms. Familismo was also found to be a significant moderator for the direct effects of attachment anxiety on …