As English has become a global lingua franca used by a greater number of nonnative speakers than native speakers, a focus on native speaker norms in English language teaching (ELT) has become obsolete. There has been a call to incorporate different varieties of Englishes (native, nonnative, and nativized) and related cultures in both teacher education programs and the English classroom- an approach known as Global Englishes Teacher Education (GELT). This study investigates the influence of a GELT-informed teacher education course offered at a US state university on the cognition and (future) practices of pre-/in-service teachers, which aspects of the GELT course had the most significant and lasting impact, and what major barriers and enablers to GELT practices participants anticipated and experienced. The data derive from pre- and post-intervention surveys and interviews, observations of the GELT course for 16 weeks, coursework, and lesson plans and materials developed/used by pre-/in-service teachers. The findings showed a positive influence of the course on participants' approach to (G)ELT and their future practices which promoted linguistic and cultural diversity. Diverse contextual factors and teacher identity influenced the cognition and practices of participants. Participants found newly learned concepts such as native speakerism, WE, and EIL particularly helpful along with course content such as conversations with English language learners and teachers, micro-teaching practices, and preparing a lesson plan with a GELT component. Participants' multilingual and multicultural identity emerged as a significant enabler of GELT practices, while diverse contextual factors were perceived as challenges to (future) GELT practices. Given the influence of the GELT course on the professional development of the participants, the findings indicate the importance of teacher education programs informed by GELT framework. The study offers recommendations to improve GELT-informed teacher education courses and proposes a model of professional development to guide teacher educators. [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.]