This book describes how Canada's Outstanding Principals (COP) processes enhanced the leadership capacities of COP recipients over and above an existing skill set, and how COP, as a leadership development program, strengthened the relationship between transformational leadership and principal efficacy. An exploratory analysis of collective principal efficacy is also presented. Concurrent, equal status mixed-methods were applied. Data were generated from two sources: online survey (including demographic items, rating scales, and open-ended questions), and telephone interviews. Insights from all ten provinces and three territories is represented in the data. Recommendations for system leaders, program developers, and policymakers are made.