This study explored experienced high school science teachers' perceptions of their positive experiences with professional learning and their impact on pedagogical beliefs and classroom practice. Semi-structured interviews were conducted with six high school science teachers from six different high schools representing four different public school districts in North Carolina. Analysis of individual transcripts using Interpretative Phenomenological Analysis (IPA) resulted in six themes: (a) "resiliency;" (b) "dissatisfaction with mandated professional learning;" (c) "feedback for learning;" (d) "reflection of impact on students;" (e) "professionalism;" and (f) "authenticity." The findings show teachers' self-selected positive professional learning experiences influenced their pedagogical beliefs and practice by strengthening or changing beliefs and classroom practices. Teachers describe their experiences with professional learning as positive when personal goals align with authentic learning tasks facilitated by expert educators, specific needs of students in their classroom are supported, and knowledgeable mentors give feedback that supports their personal learning goals. Teachers describe their experiences with professional learning as negative when there is a lack of discipline-specific science content or opportunity to be a part of the process for mandated professional learning at their schools. Teachers show increased resilience when faced with challenges and barriers during voluntary professional learning experiences in comparison to mandated experiences. As informed by complexity theory for teacher learning, the findings of this study suggest several ways teacher learning is facilitated and constrained in relationship to the individual teacher, school environment, and learning activity. Implications this can have on formal teacher learning design and research 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://bibliotheek.ehb.be:2222/en-US/products/dissertations/individuals.shtml.]