International organisations (IOs) hold important governance functions and power. Yet, they are several steps detached from the constituencies that have entrusted them with functions and resources to carry them out, even as accountability expectations remain significant for their legitimacy. This article presents a broadly generalisable theoretical framework for understanding the variable accountability of IOs, seeking to advance the understanding of international accountability in three new ways. First, it elaborates on the concept of the scope of IO accountability, which can vary across organisations, over time, and across contexts. The idea of a scope of accountability moves beyond the dichotomy of accountable versus non-accountable power holders and advances an understanding of accountability as a multi-layered phenomenon, whereby both the expectations and practices of accountability can evolve over time and with respect to different audiences. Second, the article identifies three political factors – namely the formal and informal excercise of power, institutional structure, and public salience – that can shape, in important ways, the variable scope of IO accountability. Finally, it critically explores the tensions and contradictions between these political dynamics, and the implications for access to and the efficacy of accountability systems.