Legal philosophers have taken what Ronald Dworkin called “theoretical disagreement” or disagreement about the “grounds of law,” to be of jurisprudential interest because of its putative incompatibility with legal positivism. The first aim of this article is to reframe theoretical disagreement as part of a broader challenge for all jurisprudential theories, positivist or not: how to refine and reconcile three theses that should appear plausible, important, and in tension. (1) Conventionality: the content of the law is determined, presumptively if not definitively, by meta-rules of law whose status as meta-rules arises from a consensus among relevant legal actors to treat them as having that status. (2) Disagreement: judges have theoretical disagreements about the law-i.e., disagreements about such meta-rules of law as legal interpretive methods, which they do not attempt to resolve merely by reference to explicit or implicit empirical consensus. (3) Fidelity: judges’ theoretical disagreements can be in good faith, reasonable, and legally resolvable. The article’s second ambition is to synthesize a broad range of jurisprudential writing pertinent to conventionality, theoretical disagreement, and judicial fidelity to law, in order to bring forward a potential reconciliation of all three that gives each one its due. Law and the requirements of judicial fidelity can be broadly conventional yet subject to reasonable, genuinely “theoretical disagreement” insofar as they are determined not only by contingent empirical truths about convergent practice but also by non-contingent conceptual truths about law’s nature and distinctive virtues. Unlike accounts of theoretical disagreement developed by theorists attacking or defending legal positivism, the view of theoretical disagreement I sketch here is ecumenical. It is compatible with accepting or rejecting legal positivism-though not on all positivists’ or all non-positivists’ terms.