Bandura's theory of self-efficacy has been applied in many areas of health education including smoking cessation, pain control, eating problems, cardiac rehabilitation, and adherence to regimens. Consequently, self-efficacy has emerged as an important concept with which health educators should be familiar. Self-efficacy refers to one's belief in the ability to do a specific behavior. Self-efficacy is a principle connection between knowledge and action since the belief that one can do a behavior usually occurs before one actually attempts the behavior. Self-efficacy also affects the choice of behavior, settings in which behaviors are performed, and the amount of effort and persistence to be spent on performance of a specific task. This article will examine self-efficacy theory, describe sources of self-efficacy, and present applications of self-efficacy theory.