What does it mean to say that an administrative agency is a quot;sourcequot; of law? Agencies constantly generate what we regard as law, making and remaking legal obligations at a frenetic pace. Yet many (if not most) of the rules agencies make lack the force of law and identifying those that have it is often an exceptionally difficult task. It is a task, indeed, that courts are usually not suited to performing, at least not under their present circumstances. In this article, I argue that the nature of modern legislation and our march toward bureaucratic governance and informal process have combined to render the bulk of lawmaking in our society unrecognizable in our conventional picture of legality. If legal rules are, as many modern positivists maintain, really just so many 'exclusionary reasons' by which legal actors guide their conduct, agency rules that are never enacted as such are becoming more and more of the law's content. Notice and comment was neither the beginning nor the culmination of our lawmaking's departure from easily recognizable forms. But it is perhaps the best means by which to measure the rise of a more functional concept of law in the society we actually have