Abstract: A convention is a practice not memorialized in a formal rule but regularly engaged in out of a sense of obligation, where the sense of obligation arises from the view that adhering to the practice serves valuable goals of institutional organization and the public good. Constitutional conventions are important in making it possible for the national government to achieve the goals set out in the Preamble. Over the past twenty years or so, however, such conventions have eroded. This article addresses the role and importance of constitutional conventions in the United States, arguing that conventions' erosion has been accompanied by a configuration of partisan politics that makes it difficult to present a discussion of that erosion in a way that will not itself seem partisan. I argue that contention over claims about departures from conventions takes forms familiar from ordinary common-law reasoning--perhaps not surprising because common-law reasoning rests on judicial decisions that cannot offer canonical textual formulations of the rules the courts apply. This article also discusses some of the ways in which political actors can depart from conventions, and some consequences of such departures. Finally, the Essay takes up some larger questions about constitutional transformation through abandonment or revision of constitutional conventions.