The increasing number of refugees, asylum seekers, and irregular migrants poses a challenge for mental health services in Europe. This review found that these groups are exposed to risk factors for mental disorders before, during, and after migration. The prevalence of psychotic, mood, and substance-use disorders in these groups varies but overall resembles that in the host populations. Refugees and asylum seekers, however, have higher rates of post-traumatic stress disorder. Poor socioeconomic conditions are associated with increased rates of depression five years after resettlement. Refugees, asylum seekers, and irregular migrants encounter barriers to accessing mental health care. Good practice for mental health care includes promoting social integration, developing outreach services, coordinating health care, providing information on entitlements and available services, and training professionals to work with these groups. These actions require resources and organizational flexibility.