Accountability is a pivotal concern of applied social science. This article asserts that in many situations a full explanation of the sources of accountability requires the application of concepts from sociology and management science, in addition to those from the market-based approaches inspired by economics. The article describes the market-based approach to accountability exemplified by agency theory, applies it to school reform and derives several predictions about the likely success of market-based approaches to school reform, and documents the lack of evidence supporting the contention that programs for school choice will markedly improve teacher work effort and performance (as measured by student test scores). The social actor approach, rooted in sociological and management theories, is introduced and used to describe the pressures and norms operating in the public schools that foster accountability even in the absence of competition between schools for students. The article concludes with some implications for practice and research on public sector accountability.