ABSTRACT Principal Ownership of an Instructional Initiative: Advancing a Conceptual Framework for the Study of Leadership Abigail Gray There is a need for unified theory as to how and why principals' engagement with instructional initiatives does or does not develop, and how that engagement manifests, both in specific leadership behaviors and in changes in teacher practice. Such theory could inform policy decision-making by shedding light on the mechanisms that may facilitate principals' engagement with reform initiatives, and by clarifying what that engagement might ultimately produce. This study seeks to advance a new theoretical perspective on principal behavior in the context of instructional reform by examining the implementation of a literacy intervention through the lens of principal ownership. Using structural equation modeling and targeted qualitative inquiry, the study tests a hypothesized conceptual framework for principal ownership which posits that three antecedents (control, knowledge, and self-investment) contribute to principals' engagement in ownership behavior relative to an instructional initiative. The framework further posits that this ownership behavior--specifically, change promotion relative to the initiative--leads to changes in teacher collaboration around the reform, and ultimately influences classroom practice. This framework builds upon extant theory regarding school leadership, the processes around school change, and psychological ownership. While further research is needed to confirm these findings, the results of this exploratory study suggest that the hypothesized relationships are plausible. Significant pathways are found between the antecedents and the ownership behavior, and between the behavior and teacher collaboration. Mediational analysis of the pathways between principals' ownership behavior and the reform's reported influence on classroom instruction reveals that both the direct pathway and the indirect pathway (mediated by teacher collaboration) are significant. The findings of case-study research focused on three schools largely support the SEM study's conclusions and the hypothesized relationships. Viewed together, the quantitative and qualitative findings highlight lingering questions and directions for future research.