The purpose of this qualitative exploratory single case study was to explore how professional development in blended learning influences teachers' self-efficacy in a Title I school district in the southwestern U.S. The importance of this study was to understand how teachers' self-efficacy may or may not be enhanced through professional development experience with blended learning approaches. Teachers' perceptions of their experience integrating technology after receiving professional development was significant since blended learning is transforming education. The theoretical foundation used for this study was Bandura's social cognitive theory. Purposive expert sampling was used to identify the 32 participants for this study. The data was collected through a questionnaire, interviews, and a focus group, put through a member checking process, then coded and thematically analyzed to answer the research questions. All questions posed in the questionnaire, interviews, and focus group were interlaced in a way that they answered more than one research question, and the data was analyzed from each and then all together. The findings of this study indicated that teacher efficacy increased as a result of professional development experience and the main factors that contributed to this are: teachers' sense of self-efficacy related to modeling and collaborative learning, mastery of blended learning skills and strategies through clear communication and positive feedback, and mastery in blended learning to teach self-regulatory strategies to enhance personalized learning. This study extended Bandura's social cognitive theory by seeking to understand teachers' perspectives of how professional development in blended learning influences their self-efficacy. [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.]