The purpose of this study was to investigate how Bandura's (1977) four sources of efficacy influence self-efficacy beliefs in adolescent musicians during a six-week self-modeling intervention. The study also explored the effects of a positive self-review self-modeling intervention on musician self-efficacy. Practice journals and semi-structured interviews were used to collect data from six adolescent pianists. Results indicate that mastery experience was most influential on self-efficacy beliefs in young musicians. Observing similarly skilled models, receiving positive feedback, and feeling calm or focused prior to performance increased self-efficacy in participants, while observing advanced models, making negative comparisons, and feeling anxious, distracted, or fatigued decreased self-efficacy. These results provide music teachers with several practical strategies that may facilitate stronger self-efficacy beliefs in students. Additionally, the self-modeling video increased self-efficacy when participants liked and related to their video or used the video to facilitate performance improvements. Music teachers can explore using both the performance and strategic functions of self-modeling videos as a possible tool to enhance self-efficacy in young musicians.