Many specialists have put out a call to action for more specialized training in L2 pronunciation pedagogy, as many language educators are ill-equipped to meet the instructional demands that pronunciation teaching requires (Foote et al., 2011; Henderson et al., 2015; Murphy, 2014, 2017). While language teacher professional development has started to receive attention in the field of L2 pronunciation (e.g., Burri, 2016; Buss, 2017), this conversation has not made much headway into online domains. That is, would language teacher trainees "walk" out of an online pronunciation pedagogy course with the knowledge, skills, and abilities need to teach pronunciation to their learners? To address this gap, this study investigated the development of second language teacher cognitions throughout four separate versions of an eight-week online L2 pronunciation pedagogy course using different modes of instructional delivery (i.e., PowerPoint and vignettes). In particular, this study sought to: (1) track the overall development of teacher cognitions throughout the course, (2) assess which delivery of instruction led to the most significant results, if any, and (3) track the overall efficacy of the online medium in terms of professional development in English pronunciation pedagogy. To answer the first two research questions, data collected from a knowledge questionnaire, beliefs survey, weekly narrative frames, and selected interviews were used. To answer the third research question, data collected from the beliefs survey, weekly narrative frames, and selected interviews were used. Findings showed that the participants' knowledge of English pronunciation pedagogy significantly increased, particularly in their knowledge of phonological processes and practical teaching applications. However, one dimension tested in the study (i.e., analyzing and categorizing learner errors) did not improve significantly, which suggests this knowledge base may require a more hands-on approach with experiential learning. Survey data showed that there was minimal change (only 2 of 25 beliefs showed significant change) in the participants' perceptions and beliefs about language teaching and pronunciation pedagogy. This may be due in part to the participants' experiences with language teaching, and that their beliefs had already been formed before the course started. Of particular interest was the analysis of the different sections that received various delivery of instruction. The results of a three-way ANOVA showed that course section was not significant in terms of their scores on the knowledge questionnaire. This indicates that, regardless of delivery of instruction method, participants were able to gain the knowledge delivered throughout the course. However, this study only looked at the participants' declarative knowledge (e.g., definitions) and not their procedural knowledge (e.g., actual ability to teach pronunciation). This study showed that the current professional development opportunity in English pronunciation pedagogy was overall effective, though there remains future work of improving the course based on questionnaire scores and participant feedback. Analyzing and categorizing learner errors is one problem area that future iterations of the course need to address with a more hands-on approach. Additionally, participants mentioned struggling with assessing learner progress and incorporating technology into their teaching practices--two areas that were not addressed in the current iteration. However, for pronunciation teaching, the current professional development opportunity was not only seen as desirable by language professionals across the globe, but it was also able to improve their knowledge about pronunciation terminology and teaching practices. [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.]