In Federalist 51, James Madison offered what has become the canonical account of how the separation of powers would pit branch against branch for the greater good. The officials of an institution would act on behalf of their institution for the Constitution to function properly. In Madison’s account, ensuring the presence of the right quantum of institutional loyalties would serve as a durable and plausible mechanism for enforcing institutional boundaries and ensuring a stable constitutional order. But modern scholars take a more skeptical view of his theory. This Article reconsiders the Madisonian concept of institutional loyalty as an object of analysis for constitutional scholars and jurists. Our core thesis is that institutional loyalty can be identified, evaluated, and even elicited through conscious and careful institutional design. We first provide a definition of institutional loyalty and situate the concept in the American constitutional past and present. We then marshal evidence that institutional loyalty may well have been decisive in some contemporary interbranch dynamics, even if its effects are inconstant and asymmetrical. In particular, we suggest that loyalties’ effects in the executive and judiciary are greater than their effect in the legislative context. We caution, however, that it is a mistake to view institutional loyalties as a constitutional end in themselves. Rather, institutional loyalty can promote or undermine structural constitutional goals, depending on the circumstances. Calibrating the appropriate mix of such loyalties across the branches therefore presents a considerable, if unavoidable, array of challenges. To that end, the Article offers a taxonomy of causal mechanisms by which institutional loyalty can be generated within each of the three branches. Working branch by branch, the Article identifies examples of institutional reforms capable of modifying institutional loyalty in ways that could promote widely shared constitutional ends.