Background: While numerous studies have demonstrated elevated psychosis risk in migrant groups, adequate explanations for this pattern have not been elucidated. The elevated burden of psychotic disorders represents a pressing public mental health priority, and thus understanding the determinants of increased risk is important in addressing this disparity. Objective: To determine how migration-related factors and the social environment affect the risk of developing psychotic disorders among migrants and their children. In order to investigate what drives elevated psychosis risk, my studies focused on migration-related factors, including region, age-at-migration, and family network, and aspects of the post-migratory environment, including neighbourhood ethnic density. Methods: I linked multiple Swedish population registers to conduct three longitudinal cohort studies. In Chapter 3, I investigated if risk of schizophrenia, schizoaffective disorder, and bipolar disorders varied by migrant status, region of origin, and age-at-migration. I examined the role of family network in psychosis risk amongst migrants in Chapter 4. Finally, I assessed how neighbourhood ethnic density affects psychosis risk in Chapter 5. I used Cox proportional hazards modelling throughout, with multilevel extension in Chapter 5. Results: Chapter 3 revealed increased risk of psychiatric disorders associated with migrant status was specific to psychotic disorders, with exact risk dependent on region of origin. Risk for psychotic disorders was elevated across most ages-at-migration, while risk of non-psychotic bipolar disorder was lower for all ages-of-migration except infancy. Chapter 4 showed that family networks at the time of migration differentially affected the risk of developing non-affective psychotic disorders for males and females. I found that the presence of family during migration was protective for females but increased risk among males. In Chapter 5, I found evidence that as own-group ethnic density increased, risk of non-affective psychosis decreased. Conclusions: Taken together, this research highlighted factors at the individual (e.g. migration status, region of origin, age-at-migration), family (family networks), and neighbourhood (ethnic density) levels that affected psychosis risk in migrants and their children. These studies demonstrated distinct patterns of risk and add to the body of knowledge around the social and structural explanations for psychotic disorders. These studies contribute to the growing body of evidence demonstrating the importance of the social environment in the aetiology of psychotic disorders and opens lines of inquiry for future research in this field.