WHEN PEOPLE THINK of illness, a physical problem most often comes to mind—pneumonia, diabetes, cancer, or heart disease, for example. Yet the most common diseases in society are mental illnesses, those that affect people's minds and behavior. In his book Mental Health, Mental Illness, author Lealon E. Martin writes:

Mental illness strikes more frequently, attacks more people, requires more prolonged treatment, causes more suffering by the individual and by his family and friends, wastes more human resources, takes up more buildings and other facilities, and consumes more of the personal finances of the individual and his family and the public taxes than any other disease.

Statistics show this to be the case not only in the United States but also in most other industrialized and developing countries.

Millions of people have experienced mental or emotional illnesses themselves or at close range. Mental illness has been defined...