The purpose of this study included systematically identifying commonalities in the leadership qualities of successful principals, analyzing the relationships among these qualities, and studying how the qualities vary and interact across school contexts. This study explored how successful principals acquire and apply these qualities to achieve school and student success and how leadership qualities influence school processes in different contexts. This study used meta-synthesis involving thematic analysis and meta-ethnography techniques to analyze 79 studies from 17 countries in the International Successful School Principalship Project. Leadership qualities are the personal and professional attributes that enable principals to successfully lead their schools by shaping school processes and giving rise to school practices moderated by multiple interlayered contexts. Successful principals' leadership qualities are inherent but learnable, dynamic, and adaptive. Leadership qualities are interdependent and include a combination of cognitive, psychological, ethical, social, and motivational resources, skills, and contextual intelligence. Cognitive and ethical resources are vital to developing other categories of leadership qualities. There are 13 identified relationships among the six categories. Contextual factors subtly influence leadership qualities, leading to differences in specific characteristics within each category. Contextual factors primarily shape principals' values/beliefs, and priorities in school. Microsystems have more influence on their leadership qualities than the other ecological systems. The leadership qualities contribute to eight leadership practices. Ethical, skills and psychological resources are primary categories that influence school processes and leadership practices. Six resources directly contribute to school processes or are moderated by leadership practices. The model elucidates three distinct pathways. First, leadership qualities directly influence successful principalship, with this relationship moderated by five interlayered contextual factors. Second, leadership qualities directly influence the school processes that facilitate successful principalship, moderated by the five contextual layers. Third, leadership qualities contribute to school processes by generating specific leadership actions or practices that ultimately lead to successful principalship, moderated by the same five interlayered contexts. Future studies are needed to address how to make standards and processes for developing leadership qualities and preparing principals for success and how to apply these standards and processes. [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.]