Accountability has become an increasingly popular concept in global health policy and practice in recent decades, spanning activities such as governance and cooperation, finance, and service delivery. As both a concept and a process, accountability evokes participation, transparency, and responsiveness and infers legitimacy on those actors deemed accountable for their actions. It remains contested conceptually however and is frequently put into practice in a varied set of ways—its meaning has diversified and evolved, while at the same time it has been applied to a widening range of contexts, relations, and practices. Drawing on the global governance and policy literature, specifically applied to global health systems, policy, and practice, this chapter begins with an introduction to the concept of accountability and outlines common mechanisms and instruments aimed at promoting it. Furthermore, accountability will be discussed in the context of complex global health arrangements, processes, and the exercise of power. This will be illustrated by focusing on global health partnerships in general, and more specifically the Global Fund to Fight AIDS, Tuberculosis, and Malaria as an example of such partnerships and the complex accountability ecosystems they operate within. The chapter concludes with discussion on the evolving field of global health in the pandemic era, and the challenges this poses for existing accountability mechanisms.