Unrecognized conventions—practices that are conventional even though their participants do not recognize them as such—play central roles in shaping our lives. They range from the indispensable (e.g. unrecognized linguistic conventions) to the insidious (e.g. some of our gender conventions). Unrecognized conventions pose a challenge for accounts of conventions because it is difficult to incorporate the distinctive arbitrariness of conventions—the fact that conventions always have alternatives—without accidentally excluding many unrecognized conventions. I develop an Accessibility Requirement that allows us to account for both arbitrariness and unrecognized conventions. Specifically, I argue that a conventional practice must have at least one alternative that is at least approximately as good and at least approximately as accessible as the conventional practice itself, independent of the dominance the practice gained as it became conventional. In the course of arguing for this requirement, I also show that two prominent accounts of conventions, David Lewis’s and Ruth Garrett Millikan’s, run into problems with capturing the arbitrariness of conventions. The Accessibility Requirement opens the door to improved accounts of conventions by precisely identifying the way in which conventions are arbitrary.