The music student teaching experience is a crucial time for pre-service music teachers to apply concepts they learned in university coursework to teaching practice before beginning their careers. Examination of this important aspect of music teacher education may elucidate problems of teacher attrition and feelings of unpreparedness to teach in early-career music educators. In education research, teacher self-efficacy is associated with positive teaching outcomes and feelings of preparedness to teach; learning about the teacher self-efficacy of student teachers before and after the student teaching experience can inform stakeholders working to improve the music student teaching experience and music teacher education in general. That is why the purpose of this study was to describe music student teachers' teacher self-efficacy and the sources of that self-efficacy. I sent a quantitative measure of teacher self-efficacy and sources of self-efficacy to music student teachers from 22 colleges and universities in 13 states across the United States at the beginning and end of their student teaching experience. Thirty-eight participants responded to both surveys. After comparing their pre- and post-test teacher self-efficacy scores for instructional strategies, classroom management, and student engagement, I found that participants' scores increased significantly with a large effect size for all components of teaching. Self-efficacy for instructional strategies was significantly higher than the other components. There were no significant differences in teacher self-efficacy of music student teachers when grouped by music subject or grade level taught. According to results of backward stepwise linear regression analyses, in the pre-test, mastery experience was the strongest predictor in the best model for teacher self-efficacy. Physical and emotional state, mastery experience, and social persuasion were the strongest predictors in the best model of teacher self-efficacy in the post-test data. To build teacher self-efficacy in students, music teacher educators and cooperating teachers might facilitate guided mastery teaching experiences, support student teachers with overwhelming emotions related to transitioning into the profession, and provide specific and honest feedback regarding student teachers' teaching ability throughout the experience. [The dissertation citations contained here are published with the permission of ProQuest LLC. Further reproduction is prohibited without permission. Copies of dissertations may be obtained by Telephone (800) 1-800-521-0600. Web page: http://www.proquest.com.bibliotheek.ehb.be/en-US/products/dissertations/individuals.shtml.]