While pedagogical content knowledge (PCK) has been widely studied in the literature, there have been few studies that focus on content knowledge exclusively, and none that examine the interactions between new content knowledge and existing PCK. This study traced the interactions between five teachers' pedagogical content knowledge and novel content as they implemented lessons from a professional development program in their classrooms. Case studies were created for each participant, and major themes were compared across all cases. This study found that pedagogical knowledge, knowledge of students, and knowledge of content all played major roles in the implementation process and, in turn, were impacted by implementation. Assessment was found to play little to no role in how teachers implemented a lesson. Implications and recommendations for professional development are discussed. [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.]