This article explores the cultivation of collegial trust as a central feature of the capacity-building work of 11 high school principals, nominated for their expertise with capacity building. This qualitative study examined interview data and school documents collected over 18 months. Principals regarded trust as critical and were motivated to engage in trust building based on their understanding of the importance of trust or by information that pointed to school-wide trust concerns. To address collegial trust concerns, principals set, enforced, and reinforced norms of interaction. Based on a review of interdisciplinary literature on trust development, and drawing upon a knowledge-based model of trust development where repeated interactions serve as a key mechanism for trust formation in organizations, three broad actions, emanating in large measure from principals' work to support and enhance collaboration, are identified as important with respect to the cultivation of collegial trust. Varied and context-specific strategies are noted. (Contains 8 notes and 2 tables.)