Collective teacher efficacy has gained growing attention in the field of teacher education due to its potential to enhance student experiences and life chances, as well as foster positive teaching practices and dispositions. It is believed that an inquiry-based learning community provides a promising environment for the development of collective teacher efficacy. However, limited studies have specifically examined the development of collective teacher efficacy among educators who engage in professional learning within contexts such as inquiry communities. In response, this case study was conducted in order to investigate the development of collective teacher efficacy among educators who were engaged in a practitioner inquiry community within the context of a graduate seminar. This study features a case analysis of collective teacher efficacy in a practitioner inquiry community. Four educators were selected as primary participants, while five were selected as secondary participants. They all completed a series of five semi-structured interviews, which served as the study's primary data sources. Secondary data sources included artifacts, field notes, and analytical memos. Data from these multiple sources was analyzed using a framework designed to study collective teacher efficacy within a specific context. This analysis led to the generation of themes to describe the contextual factors of the inquiry community, the aspects of experiences that tapped into the efficacy-shaping sources in the inquiry community, and the educators' beliefs regarding collective teacher efficacy in this specific inquiry community. The findings of this study reveal the intricate processes of collective teacher efficacy development and demonstrate the value of collective teacher efficacy development for educators. All sources of collective teacher efficacy are evident and influential. The findings suggest a need to reconceptualize the four sources in an expanded view of educators' professionalism. The study's findings also indicate the need to design inquiry communities in a direction that develops collective teacher efficacy serving both students and educators. This study contributed to the literature by documenting how the four efficacy-shaping sources played out in an inquiry community. [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.]