This article is primarily a study in the history of the concept of efficiency. It is argued that efficiency originated in Aristotelian ideas about causality and acquired a broad, substantive meaning of “moving force. ” This meaning of the term was dominant well into 20th-century studies of public administration. In the course of the 20th century, however, efficiency became predominantly understood as “technical efficiency”: a ratio between resources and results. This connotation is especially clear in the explicit “textbook ” definitions of efficiency. Nevertheless, we claim that the substantive meaning of efficiency is still around, and even at the heart of much criticism of efficiency. Technical efficiency obscures that efficiency in publ...