Mental health is a level of psychological well-being or an absence of mental illness. It is the “psychological state of someone who is functioning at a satisfactory level of emotional and behavioural adjustment”. For thousands of years, humans have tried to explain and control problematic behaviour. But our efforts always derive from theories or models of behaviour popular at the time, and the purpose is to explain ‘why someone is like that’. Mental illnesses are more common than cancer, diabetes, or heart disease. Over 26 percent of all Americans over the age of 18 meet the criteria for having a mental illness. Maintaining good mental health is crucial to living a long and healthy life. Good mental health can enhance one’s life, while poor mental health can prevent someone from living an enriching life. This educational book will help readers to get knowledge about various psychological disorders.