Although the link between classroom instructor behavior and student engagement has been well documented, the same cannot be said for instructors and students interacting with one another in clinical settings. Given the relatively close nature of the student-clinical instructor (CI) relationship and the considerable differences between the structured environment of the classroom and the unpredictable and often stressful environment of the healthcare clinic, classroom-based assumptions of what constitutes effective or ineffective teaching behavior may or may not be valid for the clinic. This study applied self-determination theory to investigate the degree to which CI psychological need-supporting/thwarting behaviors affect student clinical engagement. An online survey consisting of items from established scales recognized to measure teacher autonomy-, competency- and relatedness-supporting/thwarting behavior was used to question 751 undergraduate students who were currently enrolled in the clinical portion of their education in one of four radiation science disciplines (radiologic technology, radiation therapy, diagnostic medical sonography, and nuclear medicine technology) at one of 387 institutions of higher education across the United States. Correlational and linear regression analysis revealed a strong connection between overall CI need-supporting/thwarting behavior and student clinical engagement (r(749) = 0.75, p = .0000 and Delta R[superscript 2] = 0.5181, pr > F = 0.0000). The study also revealed CI relatedness-supporting/thwarting behaviors to have the most influence on student clinical engagement (beta = 0.4197, p = 0.000), followed by autonomy-supporting/thwarting behaviors (beta = 0.1298, p = 0.001) and competency-supporting/thwarting behaviors (beta = 0.1110, p = 0.007). A number of key student background factors proved to have very little or no influence on student clinical engagement. The results of this study brings awareness to the powerful impact clinical instructors have on their students' motivation to engage in educationally productive clinical activities and serves to underscore the need for routine in-service programs specifically designed to teach CIs how to effectively employ psychological need-supporting behaviors and avoid psychological need-thwarting behaviors when working with their students. [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.]