Self-effi cacy refers to the subjective conviction that one can successfully execute the courses of action required to obtain a desired outcome. Bandura (1977) rst coined the term after his experiments on phobia treatment. A group of individuals suffering from severe snake phobia participated in a treatment program. One group of these individuals directly engaged in fearful encounters with a boa constrictor, which involved mastery of progressively more fearful interactions with the snake. Another group observed a model successfully demonstrating a range of approach behaviors toward the snake. The other group did not receive any treatment. Repeated mastery experiences of the rst group and repeated observations of the model’s successes in handling the boa constrictor by the second group increased the participants’ self-ef cacy beliefs that they could handle the snake successfully. The greater were the changes in their self-ef cacy beliefs, the greater the changes in their behaviors toward the snake. The group that did not receive treatment failed to reach target performance.