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 rates of psychotic, mood and substance use disorders in these groups are variable but overall are similar to those in the host populations; however, the rates of post-traumatic stress disorder in refugees and asylum seekers are higher. Poor socioeconomic conditions are associated with increased rates of depression five years after resettlement. These groups 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.