This phenomenological study demonstrates the influence that affective factors have on beginning teachers' ability to enact instructional practices. Through narratives shared in interviews and web log postings, two beginning science teachers' emotional engagement with their instructional practices, especially that of implementing inquiry-based instruction, and the resulting impact these emotions had on professional decision-making were evidenced. Anxiety emerged as the most significant impacting emotion on instructional decision-making with the participants. Through their stories, the two participants describe how their emotions and views of self influence whether they continue using inquiry pedagogy or alter their lesson to adopt more didactic means of instruction. These emotions arise from their feelings of being comfortable teaching the content (self-efficacy), from the unpredictability of inquiry lessons (control beliefs), from how they perceive their students as viewing them (teacher identity) and from various school constraints (agency). This research also demonstrates how intertwined these aspects are, informing each other in a complex, dialectical fashion. The participants' self-efficacy and professional identity emerge from their interactions with the community (their students and colleagues) and the perceived agency afforded by their schools' curricula and administration. By providing descriptions of teachers' experiences enacting inquiry pedagogy, this study expands our understanding of factors that influence teachers' instructional practices and provides a basis for reforming science teacher preparation. [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.]