Background/Context: Partnering across districts, schools, and other community organizations has become ubiquitous as a policy for promoting change. Despite growing attention to and scholarship on district-community partnerships, there is little examination of the organizational mechanisms involved in sustaining them. Purpose/Objectives: This study examines the ways in which district-community partnerships establish and sustain legitimacy with multiple constituencies over time. Drawing on institutional theory, these analyses extend current theories of legitimation by describing the legitimacy-building events of districts and their community partners as they craft partnerships over time. Research Design: I used a qualitative multi-case-study design to build grounded theory based on three district-community partnerships. Interviews with partnership leaders, focus groups with governance team members, and observations were collected between 2012 and 2014. Thematic analysis was conducted within and across the three cases to identify legitimacy-building activities. Findings/Results: Five mechanisms for building legitimacy emerged across the three district-community partnerships: funder endorsement, attention to reciprocity, service provision, dedicated formal staff roles, and a systems-building approach. Each mechanism was deployed across the stages of partnership (e.g., identity formation, recruitment, sustainability). These mechanisms were used to leverage legitimacy with one stakeholder group to build new legitimacy with other stakeholder groups, creating complex chains of legitimacy across partners over time. Conclusions/Recommendations: The findings extend current research on both legitimacy frameworks and the use of community partnerships in education reform. Themes across cases highlight the recursive nature of legitimacy during the recruitment of new partners, how partnerships can build legitimacy across cultural divides, and the role of external funders in supporting legitimacy building across multiple sets of stakeholders.