Professional training for language instructors needs to be more accessible and high-leverage in order to meet the growing demand for proficient users of Chinese, Korean, and Japanese languages. More specifically, teachers of these languages need exposure to effective teaching methods designed to meet the language-specific needs required to help learners achieve higher language proficiency. One such teaching approach is called Comprehension-based Instruction (CBI). CBI is a collection of language teaching approaches and practices that, according to researchers, is based on the idea that observing language in use, through listening, reading, or seeing language signed, is necessary for language development to occur. Studies suggest learners who learn through CBI have increased language proficiency compared to learners learning through many other methods. However, despite the growing evidence in support of CBI approaches, few instructors of Chinese, Korean, and Japanese languages have the opportunity to learn about CBI. One way to expose more language instructors to CBI is through online teacher professional development (oTPD) training. This Design-Based Research (DBR) study aimed to design and evaluate an oTPD training program for Chinese, Korean, and Japanese language teachers that focused on teaching CBI. The purpose of the study was to gain insight into the characteristics of an oTPD training that led to desirable mediating processes and outcomes. The study drew on Experiential Learning Theory (ELT) and followed three DBR design stages: alpha, beta, and gamma. Participants in each design stage consisted of expert reviewers and teacher participants. The results of this study suggested that the Experiential Learning Theory (ELT) model was an effective model for an oTPD training, the participants valued learning alongside similar-language teachers, and there was a significant change in teachers' practice and ability beliefs from participating in this oTPD training. This study generated an ELT-based design model for future oTPD trainings. Overall, the insights gained from this study have provided support for the importance of using DBR to design and evaluate online learning environments. Recommendations for future research using DBR include designing online learning environments with the ELT-framework and adopting this study's design model to develop and evaluate oTPD trainings. [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.]