While nonprofit organizations and their brands are growing in importance and stature, these organizations display surprisingly limited brand management activities. This is partly due to the fact that no explicit brand equity models exist specifically for nonprofit organizations. The aim of this research is to build a formal model of brand equity for international nonprofit organizations engaged in development, advocacy and relief work, using a combination of a system dynamics approach and grounded theory development. In doing so, we hope to contribute to the system dynamics literature by illustrating the step-by-step process of building a model from actual case studies rather than the traditional approach of literature review. Based on in-depth field work in three organizations (Care, Oxfam, and World Vision), two waves of focus groups with 18 brand managers led to the derivation and validation of a formal brand equity model. At the heart of this model are four core variables (Consistency, Focus, Trust, and Partnerships) and their associated causal loops. As such, this research constitutes a significant attempt to advance our understanding of brand equity in nonprofits through modeling, and to demonstrate the effective use of system dynamics in areas of marketing that have traditionally not considered this methodological approach.