The Building Castles Together project is a multidisciplinary collaboration between the University of Southern Maine at Lewiston-Auburn College and Sandcastle Clinical and Educational Services that aims to build solidarity and resilience in vulnerable young children, their families and their community. This article explores how the partnership exemplifies five key areas impacting the sustainability of community-university collaborations. 1) Mutuality and reciprocity are foundational elements in establishing trust and ensuring project relevance to both organisations. 2) Interdisciplinarity and diversity are constructs related to the core mission of both the University and Sandcastle. The multiple perspectives offer a range of holistic strategies for addressing complex social problems, but also create the potential for misunderstandings between disciplines and organisations. 3) Community integration at multiple levels is critical to the partnership’s sustainability as well as to achievement of its ideals. 4) Dynamic interaction is an evolutionary process, both internal and external to both organisations, that impacts their relative contributions and necessitates flexibility in planning and outcomes. 5) Asset enhancement describes the potential to increase capacity, but also the concern for overextension and resource exhaustion. We conclude that sustainability in university-community partnerships is not a goal in itself, but an ongoing process, and an attribute of a partnership based on common principles, continuous input and constant change.