Abstract Is it possible to build a global organization based on the model of a social movement? We analyze Project ECHO (Extension for Community Healthcare Outcomes), an entity with over 4 million participants in 193 countries, which claims to have operated with a social movement-like structure for over two decades. In so doing, it has achieved significant scale in addressing an entrenched social problem: the lack of specialized healthcare and social services in underserved communities. Utilizing interviews and other qualitative data sources to develop an analytic case study, we identify four features in Project ECHO’s model that collectively appear to enable it to balance mission, legitimacy, permanency, and scale, to a greater degree than either a social movement or a traditional third-sector organizational model might. Its organizing structure may enable operation with a permanence social movements lack, while reducing some challenges organizations often face in simultaneously maintaining mission and stakeholder legitimacy at lasting global scale.