Epidemiological studies related to the field of migration have demonstrated that rates of psychotic disorders among some migrant groups are higher than expected. This chapter explores the factors related to returning migrants and internal migration. One of the major aspects of social changes following rapid globalisation from the second half of the last century is migration. Most studies used a cross-sectional design and assessed short-term and/or long-term effects of migration on mental health retrospectively. The time of investigation is a key issue in assessing the impact of migration on mental health. Earlier studies among immigrants suggested a negative migration effect on people who were in the early incipient stage of illness, notably schizophrenia, prior to migration. Influenced by both biological and psychological factors, cultural and social changes arising from migration may put vulnerable migrants at risk for developing mental problems.