The separation of powers may be the most central idea in the theory of institutional design. Yet this has only been true of thinking about public institutions. The autocrat of the state was seen as the threat to our freedom. As a result, when we think of the separation of powers today, we think of separations among these branches of the state – the legislature, the executive, and the judiciary. The method in the chapter is not to analyze the history of the idea of the separation of powers. The republican idea of checking power with countervailing power is often read as a deterrence model for controlling abuse of power. An interesting implication of this for republican political theory is that the separation of powers and dialogic appeals to the virtue of citizens are not just separate republican ideals. A standard rationale for the separation of powers is deterring abuse of power with countervailing power.