Mental health may be measured in terms of an individual's abilities to think and communicate clearly, learn and grow emotionally, deal productively and realistically with change and stress, and form and maintain fulfilling relationships with others. Mental health is a principal component of wellness—self-esteem, resilience, and the ability to cope with adversity influence how people feel about themselves and whether they choose lifestyles and behaviors that promote or jeopardize their health.

Mental illness refers to all identifiable mental health disorders and mental health problems. Mental Health: A Report of the Surgeon General, 1999 defines mental disorders as "health conditions that are characterized by alterations in thinking, mood, or behavior (or some combination thereof) associated with distress and/or impaired functioning." The report distinguishes mental disorders from mental problems, describing the signs and symptoms of mental health problems as less intense and of...