Public policy instrumentation and its choice of tools and modes of operation are treated either as a kind of evidence (governing means making regulations, taxing, entering into contracts, communicating, etc.) or as if the questions it raises (the properties of instruments, justifications for choosing them, their applicability, etc.) are part of a rationality of methods without any autonomous meaning. This paper aims to explain the significance of a political sociology approach to public policy instruments in accounting for processes of public policy change: (1) public policy instrumentation is a major issue in public policy, since it reveals a (fairly explicit) theorization of the relationship between the governing and the governed: every instrument constitutes a condensed form of knowledge about social control and ways of exercising it; and (2) instruments at work are not neutral devices: they produce specific effects, independently of the objective pursued (the aims ascribed to them), which structure public policy according to their own logic.