Accountability is a central feature of any rights-based approach to health because it converts passive beneficiaries into claims-holders and identifies states and other actors as duty-bearers that can be held responsible for their discharge of legal, and not merely moral, obligations. This article reviews what we mean by accountability, how courts and other mechanisms are being engaged to promote accountability, and what we should understand as the central obligations of states and other actors if we are concerned with obligations of progressive realization relating to health and development goals. The first part of the article sets out a number of mutually-reinforcing dimensions of accountability, examines different duty-bearers, and discusses mechanisms for enforcement, with a focus on courts. The second part of the article explores how we might define the obligations of progressive realization for which we seek accountability. I argue that there are three aspects of accountability with which a human rights approach to health as a social policy and development issue should be concerned: (1) what the state is doing; (2) how much effort the state is expending; and (3) how the state is going about the process. Although the focus is on national obligations, I argue that donor states and other actors have parallel obligations.