Over the last three decades, the Arctic and the Arctic Council (AC) have experienced profound changes. Since its establishment in 1996, the AC has evolved significantly in reach and stature; it has expanded its portfolio of projects and instruments, and it has also substantially enhanced its administrative capacities. So far, most studies on the AC have focused on exogenous sources of its change. In contrast, drawing from the general literature on international environmental regimes and gradual institutional change, this paper examines the endogenous factors and properties of the AC and the role they play in enabling or constraining the AC’s institutional change. This reveals that the AC’s setup provides ample space for change agents who, if able to identify windows of opportunity and exploit the inherent openness of the Council’s rules, can establish new precedents that can ultimately influence the course of the AC’s evolution. As such, the analysis draws our attention to previously understudied questions of agency and endogenous sources in the processes of institutional change of the AC. Moreover, as a case study on an informal institution, it is a source of insight and a contribution to the general literature on international environmental regimes, which to date has focused almost exclusively on hard-law and treaty-based institutions.