It has been widely documented that the process of migration may contribute to negative psychological outcomes (Bhugra, 2004; Cantor-Graae & Selten, 2005). Although there are approximately 150,000 Polish citizens living in the Republic of Ireland and Northern Ireland, the research on their mental health is surprisingly modest. The main aim of the thesis was to estimate the psychological status of Polish migrants in Ireland through examination of associations and mechanisms concerning demographic, psychological, and migration related variables. A paper survey comprising of a selfreported assessments was applied to collect the data among the Polish migrants and the Irish natives. The project's results indicated that the status was relatively positive. When the Polish group (N = 354) was compared with the Irish native residents (N = 304), there were no significant differences noted on depression, anxiety, and stress levels. This finding supports past research indicating that there is no unequivocal evidence of increased levels of mood disorders when migrants are compared with native populations (Swinnen & Selten, 2007). Although Poles scored higher on some dimensions of psychotic-like experiences when compared with the Irish participants, the differences were relatively modest. As psychosis was found to be often associated with increased levels of mood disorders (Cosoff & Hafner, 2008) and no such associations were found in the project's results, a substantial increase of psychotic-like experiences is not expected in future regarding the Polish migrants. However, it is important to emphasize that past evidence indicated that psychosis-related, psychologically negative outcomes were 'stronger' for second generations of migrants when compared with first generations of migrants (Cantor-Graae & Selten, 2005). The differences pertaining to social resources, early trauma, and substance abuse were small and as such did not seem to pose serious problems for the Polish migrants. Moreover, psychometric properties of the DASS-21 (Lovibond & Lovibond, 1995) scale and its measurement invariance across gender and nationality were confirmed. Furthermore, it was found that social capital plays an important role as a mediator between the migrant class and mental health. Finally, the association between social capital and mental health was dependent on the migration status prior migration. The findings of the thesis have important practical implications. Apparently, not all types of migration result in a worsened psychological status of migrants. It is likely, that the migrant groups characterised by relatively high education qualifications and language skills, and equipped with a similar legal status as native residents may function well outside their countries of origin. Moreover, the project's findings may result in reduced discrimination and more positive views of migrant groups. The heterogeneity of the Polish group defies the view that migrant groups are homogeneous and characterised by uniform features. Additionally, the identified heterogeneity may have important practical implications as it was established that members of the 'Traditional' class were characterised by higher levels of anxiety when compared with members of the 'Established' class. Despite relatively positive findings pertaining to the psychological status of Poles in Ireland, it should be noted that perhaps some Polish migrants characterised by poor mental well-being might have been underrepresented in the project's sample. Cross-sectional design and representativeness of the samples constitute the two main methodological limitations of the project.