This study proposed that when professional development modeled the inquiry-approach and provided time for peer-observed enactment and reflection, it would produce change in in-service chemistry teachers' beliefs and practices. Case study methodology was used to collect a variety of in-depth data on teachers' beliefs and practice including interviews, journals, classroom videotape and participant-observation by the researcher to address the research questions: (1) How does the use of an inquiry approach with in-service chemistry teachers in a professional development result in their re-examining their pedagogical theories? (2) How does the reflection on the inquiry approach and practice teaching result in changes in these teachers' pedagogical theories? (3) How do the changes in these teachers' pedagogical theories translate into their classroom practice? Semi-structured interview data reveals 7 of 9 in-service chemistry teachers showed evidence of change in their beliefs over a year-long professional development (PD) program. Reflection data from the participating teachers showed they believed that modeled inquiry placing them in the student-learner role helped them to re-examine their pedagogical theories and develop more inquiry-based beliefs. Additionally, the professional development's emphasis on collaboration, peer-observed enactments, guided reflection, and the establishment of a community of learners helped them to re-examine their pedagogical theories and develop more inquiry-based beliefs. RTOP data revealed that 5 of 9 in-service teachers translated their beliefs into inquiry practice in their classrooms. [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.]