Teaching and learning have been a focus of professional development for community college faculty, yet little is known about the impact of professional development on the instructional practices of part-time community college faculty. The purpose of this qualitative study was to describe the impact of sustained professional development on the instructional practices of part-time community college faculty members. The theoretical framework for this study was grounded in Knowles's theory of adult learning, which suggests that people who are self-directed and who take responsibility for their own learning produce stronger results. A comparative case study design was used to purposefully select 4 part-time community college instructors who participated in a 24-week teaching seminar at a large community college. Data were collected from multiple sources, including individual interviews, observations of instruction, and online reflective journals. Single case data were inductively coded and categorized, and a cross case analysis was conducted to determine emerging themes. Findings suggested that a teaching seminar produced a positive impact on instructional practices for part-time instructors who found their voice in the community college environment and who developed competencies in instructional planning and design. A primary recommendation was to recognize the role part-time faculty play in improving student learning and to implement sustained support for these instructors as they seek to improve their instructional practices. Implications for positive social change include use of the results to develop a professional development model that can result in improved teaching and learning. [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://bibliotheek.ehb.be:2222/en-US/products/dissertations/individuals.shtml.]