Extant literature associates the central purpose of open strategizing with organizations seeking to manage legitimacy (e.g. Chesbrough & Appleyard, 2007; Whittington, Cailluet & Yakis-Douglas, 2011; Dobusch, Dobusch & Muller-Seitz, 2017). To date, legitimacy has been highlighted as a potential 'effect' (Gegenhuber & Dobusch, 2017) or 'outcome' (Luedicke, Husemann, Furnari & Ladstaetter, 2017) of strategic openness. Absent has been research attempting to understand open strategy as a process of legitimation (Uberbacher, 2014), and there remains a need to elevate the potential of open strategy for managing legitimacy further. To address this gap, the research presented here adopts a longitudinal, single case analysis to explore a professional association who developed a new four-year strategic plan using an open strategy approach. The findings indicate how open strategy dynamics represent the case organization switching between distinct approaches to legitimation, to manage competing stakeholder demands. The research offers an important contribution by accentuating the principal relevance of organizational legitimacy in open strategizing. This brings open strategy into close alignment with organizational legitimacy literature and its theoretical