Authority has long been associated with leadership, but the relationship between authority and leadership has remained elusive. Addressing the issue of the interplay between authority and leadership, this paper builds on limited recent work that has considered leadership to be an in situ accomplishment in which the doing of authority is interwoven with the doing of leadership. Using transcripts of real-time interaction taken from a Board meeting of an NGO, and applying the Montreal School’s ventriloquial approach to the analysis of organisational communication, the research question this paper asks is: what authorises one of the Board members to ‘take the lead’ in establishing measures to ensure that the actions of the NGO are sustainable? Findings suggest that it is neither position, nor expertise, that authorise leadership. Rather, it is the articulation of the ideal of sustainability. Leadership is thus shown to be both a question of human leaders and ideals that they are able to mobilise which authorise their claim to leadership.