This article strives to articulate some of the conventional foundations of law. The article consists of three main arguments. First, between H. L. A. Hart's conception of the rules of recognition and H. Kelsen's theory of the basic norm, Hart's view is more compelling. Second, the paper argues that the rules of recognition are social conventions but not of the familiar coordinative type, as some commentators have claimed. Finally, the article draws a distinction between deep and surface conventions, arguing that there are some deep conventions about what law is, and surface conventions that determine what counts as law in a particular community. This distinction between deep and surface conventions is employed to solve some of the puzzles about the nature of the rules of recognition.