The renowned psychologist Albert Bandura’s theory is that those with high self-efficacy expectancies (the belief that one can achieve what one sets out to do) are healthier, more effective and generally more successful than those with low self-efficacy expectancies. The author begins with a discussion of theory and method and then examines how belief in one’s abilities affects development, mental functioning and health, with examples from the areas of psychopathology, athletics, business and international issues.