With increasing global migration, research has paid greater attention to acculturation of immigrant population in relation to psychological well-being and stress. Yet, research on immigrant employees and international students especially in non-western, developing countries is relatively overlooked. To extend previous research, the aim of the present thesis is to examine the associations between acculturation orientations and attitudinal outcomes of the two populations of immigrants- immigrant employees and international students. Study 1 investigated the relationships between acculturation orientations and three dimensions of organisational commitment of immigrant employees in Thailand and England. The results demonstrated the moderating effect of organisation type (i.e. multinational vs. non-multinational) on the links between acculturation orientations and organisational commitment which were mediated by organisational identification (i.e. moderated mediation model). Study 2 extended the results of Study 1 by examining perceived ethnic similarity as a moderator and by including ethnic identity as an additional antecedent to the previous framework. The results replicated Study 1 which suggested a positive association between heritage culture orientation and organisational commitment through identification when immigrant employees in Thailand perceived high ethnic similarity in workplace. In contrast, when employees perceived low ethnic similarity, identification with mainstream culture has a positive association with the affective and normative facets of organisational commitment. Study 3 responded to the Interactive Acculturation Model (IAM) which describes acculturation as a two-way phenomenon by examining acculturation orientations of both domestic and international students in Thailand and England. The findings indicated three-way interactions (1) between perceived cultural distance and two acculturation orientations and (2) between intergroup contact and two acculturation orientations on college self-efficacy and university attachment respectively. Cultural differences between acculturation orientations of international students were potentially explained by multicultural environments in higher education and by domestic students' expectations of international students' acculturation orientations. Together, the thesis provides empirical evidence for a more comprehensive understanding on the associations (1) between acculturation orientations and work attitudes of immigrant employees and (2) between acculturation orientations and international students' sense of belonging and confidence to perform in a university life across the two countries.