BackgroundAccountability in global health is a commonly invoked though less commonly questioned concept. Critically reflecting on the concept and how it is put into practice, this paper focuses on the who, what, how, and where of accountability, mapping its defining features and considering them with respect to real-world circumstances. Changing dynamics in global health cooperation - such as the emergence of new health public-private partnerships and the formal inclusion of non-state actors in policy making processes - provides the backdrop to this discussion.DiscussionAccountability is frequently reduced to one set of actors holding another to account. Changes in the global health landscape and in relations between actors have however made the practice of accountability more complex and contested. Currently undergoing a reframing process, participation and transparency have become core elements of a new accountability agenda alongside evaluation and redress or enforcement mechanisms. However, while accountability is about holding actors responsible for their actions, the mechanisms through which this might be done vary substantially and are far from politically neutral.Accountability in global health cooperation involves multipolar relationships between a large number of stakeholders with varying degrees of power and influence, where not all interests are realised in that relationship. Moreover, accountability differs across finance, programme and governance subfields, where each has its own set of policy processes, institutional structures, accountability relations and power asymmetries to contend with. With reference to the Global Fund to Fight HIV/AIDS, Tuberculosis and Malaria, this paper contributes to discussions on accountability by mapping out key elements of the concept and how it is put into practice, where different types of accountability battle for recognition and legitimacy.SummaryIn mapping some defining features, accountability in global health cooperation is shown to be a complex problem not necessarily reducible to one set of actors holding another to account. Clear tensions are observed between multi-stakeholder participatory models and more traditional vertical models that prioritise accountability upwards to donors, both of which are embodied in initiatives like the Global Fund. For multi-constituency organisations, this poses challenges not only for future financing but also for future legitimacy.