This article explores the cultural narratives through which members of organizations define legitimacy during prolonged periods of change. We view legitimacy work as a cultural practice and interpretive process that takes the form of organizational narratives. We show how the shifting configurations of internal power relations shape both the choice and the meaning attached to the varied legitimacy narratives. We investigate the construction of legitimacy through a longitudinal case study based on participant observation of Gamma, a government Research and Development (R&D) organization, during a process of intense change. We provide theoretical insights into the construction and deconstruction of the legitimacy by analyzing the narratives in play during a process of planned change. We claim that legitimation narratives not only evolve in accordance with functional need or, in a sense, that older narratives give room to newer, more updated or relevant narratives, but also that multiple narratives are used by different organization actors alternately and interchangeably as part of internal contestation over legitimation of change.