Despite their importance, teacher's manuals (TM) have never drawn much attention in language teaching research, and therefore they have not been researched from the perspective of pronunciation teaching. It may be that they have not been perceived as having a role more than being an answer key for student materials (Sheldon, 1987). However, TMs deserve attention since curriculum materials--including TMs--have a positive impact on teachers' learning and professional development (Grossman & Thompson, 2008). TMs may especially be crucial in supporting teachers in pronunciation teaching since many teachers find this skill challenging because of lack of training (Foote, Holtby, & Derwing, 2011), lack of experience (Burns, 2006), lack of knowledge (Baker & Murphy, 2011), and lack of confidence (Bernat, 2008). This study investigated native and non-native English-speaking teachers' (NEST and NNEST) cognitions--mainly knowledge--in relation to (1) pronunciation teaching and (2) pronunciation teaching materials. In addition, the study explored (3) how teachers used an online teacher's manual (OTM) and (4) what kind of influences the OTM had on pronunciation teachers' cognitions about and confidence in pronunciation teaching. Data of this study for the first two research questions came from the survey responses of 54 teachers (NEST = 34; NNEST = 20) and interview responses of 24 teachers (NEST = 14; NNEST = 10). Data for the third and fourth research questions came from the weekly journal responses and the tracking of real-time data use of eight teachers (NEST = 5; NNEST = 3) who taught with the OTM. Findings showed that native and non-native English-speaking teachers said that lack of subject-matter knowledge or pedagogical content knowledge made pronunciation teaching challenging at times. Lack of knowledge was shown to be influential on their confidence in teaching certain pronunciation features. Examination of teachers' cognitions related to pronunciation teaching materials showed that most of the teachers used a textbook while teaching pronunciation and less experienced teachers relied on their textbooks more heavily. In line with this finding, less experienced teachers, regardless of their language background, used the OTM more strictly, and mostly for the guidance it provided rather than for the answers. The OTM was influential in increasing and refreshing teachers' knowledge of pronunciation, regardless of language and education background, and in boosting some teachers' confidence in teaching pronunciation. Additionally, the use of the OTM was influential on creating positive attitudes towards using technology in teaching for some teachers who previously preferred using printed materials. This study shows that all kinds of teachers, NESTs and NNESTs, inexperienced and experienced, trained and untrained may benefit from information presented in a multimodal format in an OTM. The OTM brings flexibility into teachers' materials preferences with its practicality and accessibility. This study shows that a TM designed in an online platform is promising for making contributions to teachers' cognitions including their knowledge, and attitudes, and therefore positively affecting their confidence as pronunciation teachers. In this, a TM can be more than just an answer key, and can also become an important contributor to the continuing development of teacher cognitions. For pronunciation teaching, where many teachers have had inadequate training, a well-designed TM can provide the support that can make their teaching more knowledgeable and effective. [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/en-US/products/dissertations/individuals.shtml.]