Psychosocial development theories propose that adolescents’ ability to form a clear and stable sense of identity; and self- regulated behavior provide the basis for their effective functioning to deal with the demands of daily life. The present study was designed based on two theoretical perspectives on the development of self-integration, namely Self-Determination Theory (SDT; Deci & Ryan, 2000) and Berzonsky’s (1990) Identity Style Model in determining the psychological well- being among adolescents. The main objective was to determine the relationship between identity styles, causality orientations and psychological well-being among adolescent. The predictive relationship among these constructs was studied across cultures i.e., Collectivistic (Pakistan), Individualistic (USA, UK, & Belgium). The study also aimed to test a proposed model of relationships through Structural Equation Modelling (SEM) across cultures. Further, the role of demographic variables i.e., gender and age was also probed. For this purpose the Revised Identity Style Inventory (R-ISI4; Berzonsky, 2007), General Causality Orientation Scale (GCOS; Deci & Ryan, 1985) and Psychological Well-Being Scale (PWBS; Ryff, 1992) were used to measure the constructs. The research was carried out in three phases. Phase-I dealt to establish the psychometric properties of all the three measures for both types of cultures. Measures were validated through Confirmatory Factor Analysis (CFA) and Exploratory Factor Analysis (EFA) for collectivist and individualist cultures. The findings suggested some modifications in instruments for Pakistani sample. Internal consistency was also determined through alpha coefficients and item total correlations for both cultures. Phase-II aimed to find out the relationship between identity styles, causality orientations, and psychological well-being across cultures. The instruments finalized in Phase-I were administered on two independent samples 500 (Pakistan) and 430 (USA, UK & Belgium) comprised boys and girls of age ranged from 15 -22 years (M= 18, SD=2.2) from different educational institutions of both cultures. The findings revealed significant relationship of information identity style with autonomous orientation, normative identity style with controlled orientation and diffuse- avoidant identity style with impersonal orientation in both cultures. The multiple regression analysis suggested significant prediction of causality orientations by identity styles; and psychological well-being as an outcome product of these styles and orientations. The t-test analysis showed significant gender differences in such a way that boys scored higher on information style and commitment in Pakistani culture whereas girls were higher on information and diffuse-avoidant style and boys scored higher on commitment in individualist culture. Similarly for causality orientation boys were high on autonomous and impersonal orientation as compared to girls who scored higher on controlled orientation in Pakistani culture whereas in individualist culture boys were higher on autonomous orientation and girls on controlled. The gender difference for psychological well-being was not appeared significant for Pakistani sample but for individualist sample girls were higher on psychological well-being as compared to boys. Significant age differences were also found for all three variables in both cultures. Additionally, current study also explored the moderating role of gender and age in the relationship of identity styles, causality orientation with psychological well-being. The findings showed significant moderation of gender and age in relationship of identity styles with psychological well-being; and causality orientation with psychological well- being in both cultures. Phase- III of the study aimed at testing the proposed model of predictive relationship between study variables across cultures. Structural Equation Modelling (SEM) was executed through Analysis of Moment Structure (AMOS) 18. The significant findings appeared for both cultures with few differences in predictive paths among variables but the entire major proposed paths were found significant as information identity style and autonomous orientation leads to high psychological well-being and diffuse- avoidant style and impersonal orientation showed low psychological well-being in both cultures. Further, it was found that causality orientation significantly mediates the path from identity styles to psychological well-being in both cultures. Implications of present study are discussed under cross cultural and theoretical framework for future research directions.