H.L.A. Hart's The Concept of Law is the most important and influential book in the legal positivist tradition. Though its importance is undisputed, there is a good deal less consensus regarding its core commitments, both methodological and substantive. With the exception of an occasional essay, Hart neither further developed nor revised his position beyond the argument of the book. The burden of shaping the prevailing understanding of his views, therefore, has fallen to others: notably, Joseph Raz among positivists, and Ronald Dworkin among positivism's critics. Dworkin, in particular, has framed, then reframed, the conventional understanding, not only of Hart's positivism, but of the terms of the debate between positivists and him. While standing on the sidelines, Hart witnessed the unfolding of not only a lively debate between positivists and Dworkin, but an equally intense one among positivists as to positivism's (and his) core claims. The most important debate has been between so-called inclusive and exclusive positivists: a debate as much about Hart's legacy as about the proper interpretation of legal positivism.