International legal accountability involves the legal justification of an international actor's performance vis-à-vis others, the assessment or judgment of that performance against international legal standards, and the possible imposition of consequences if the actor fails to live up to applicable legal standards. This article examines questions of accountability in the international legal system through the lens of the state responsibility regime. It begins with an examination of the law of state responsibility and the accountability framework that it provides. By definition, that framework can facilitate only inter-state accountability on the basis of positive legal rules. The article then turns to the increasingly rich variety of other modes of international legal accountability. The rise of these alternative modes reflects the expansion of international law's normative horizons beyond inter-state concerns, the widening of the range of international actors, and the diversification of international law-making and implementation methods. It also reflects the fact that states rarely resort to the law of state responsibility to hold one another accountable for breaches of international law. Thus, while state responsibility remains the “paradigm form of responsibility on the international plane,” it is not clear that it constitutes the paradigm form of legal accountability in contemporary international practice.