The expansion of heritage language education in the U.S. is contingent upon the improvement of heritage language teachers' knowledge and abilities in the classroom, as well as the adoption of the most effective methods for instructing heritage language learners. In order to accomplish the aforementioned goal, it is imperative to identify a set of efficient professional development supports that are geared towards enhancing the teaching skills and self-efficacy of heritage language (HL) teachers in the domains of student engagement, classroom management, and instructional strategies. This mixed-methods study examined teachers' self-efficacy and experienced with PD content through pre-and post-surveys, reflections on professional development sessions, and interviews. Data were collected from 22 teachers of less commonly taught heritage languages in community-based schools across the U.S. Descriptive statistical analysis of pre-survey provided a much-needed context in understanding HL teachers' sense of teaching self-efficacy. A series of professional development workshops were developed and offered to participating HL teachers. The study collected and examined post-PD reflections and interviews of participants with the aim to gain insights into the experiences of HL teachers during the PD sessions and to identify best techniques for PD development and organization. Findings from this portion of the study outlined four key predictors of an effective PD that impacted HL participants' experiences: (1) selection of relevant topics and focused content; (2) connection between theory and practice; (3) collaboration and active learning; and (4) inclusion of models and modeling. The study utilized statistical analysis techniques such as descriptive statistics and paired t-test samples to assess changes in teachers' self-efficacy. The results indicated that there were no statistically significant changes in teachers' self-efficacy scores in student engagement subscale. The findings revealed a medium size effect on classroom management and instructional approaches. The examination of both the quantitative and qualitative components yielded significant implications for enhancing the professional development of educators in cultivating an increased sense of efficacy in teaching high-level skills. [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://bibliotheek.ehb.be:2222/en-US/products/dissertations/individuals.shtml.]