There is a broad consensus that state capacity is central to economic and institutional development. But while the concept originated as a tool for macro-historical and comparative analysis, its success has led the term ‘capacity’ to become a default metaphor for discussing the quality of government bureaucracies. This paper discusses the limitations to conceiving of narrower questions of bureaucratic performance and policy implementation through the lens of the broad, aggregate concept of capacity. Whereas capacity refers to bureaucracies' hypothetical potential, this usually differs from their actual actions due to internal information and incentive problems created by bureaucracies' collective nature, and the constraints and uncertainty imposed by their multiple political principals. Capacity is a convenient shorthand term and is appropriate for some purposes, but it achieves this convenience by abstracting away from the mechanisms that determine bureaucratic performance and policy implementation. To advance the study of bureaucratic quality, researchers should seek to understand the implications of bureaucracies' collective nature, engage with contextual specificity and contingency in policy implementation, and focus measurement and reform efforts more towards actual performance than hypothetical capacity.