This qualitative study examines the perspectives of secondary teachers characterized as passionate on the critical incidents that shaped, negatively or positively, their levels of passion. Vallerand and colleagues describe passion as a strong inclination or desire toward an activity that one likes and finds important enough to invest time and energy in. This study is grounded in two theoretical frameworks: Deci and Ryan's Self-Determination Theory, which focuses on human motivation, personality, and development--and Lewin's Model of Change, which describes individuals' reactions to change management processes. For data collection, I conducted 60--150-minute interviews with twelve secondary teachers who were nominated by school district supervisors as passionate teachers, using an established definition. Through data analysis, I identified the themes related to this study's research questions. In regard to the first research question--on critical incidents that influenced their passion--the themes were (a) life events and transitions, (b) the impact of policies and politics, (c) social and occupational mobility, and (d) validation and affirmation. For the second research question--on internal factors that influence passion--the themes were (a) personal traits, (b) personal values, and (c) internal expectations. Lastly, the themes answering the third research question--on external factors--were (a) environmental external factors, (b) life events and transitions, and (c) cultural and societal factors. Implications for theory and practice are included. [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.]