1. Psychological disorders include mental illnesses that cause significant distress or impairment in daily life. Diagnosis can be subjective and cultural factors influence definitions of disorders. 2. The DSM-IV provides official categorization of psychological disorders in the US using a 5-axis model addressing clinical disorders, personality disorders, medical conditions, psychosocial stressors, and level of functioning. 3. Hypothesized causes of psychological disorders are often speculative and complex, with multiple genetic and environmental factors interacting in each case.