Lon Fuller, in his response to H.L.A. Hart’s 1958 Holmes Lecture and elsewhere, argued that principles of legality—formal principles requiring, for example, that laws be clear, general, and prospective—constitute the “internal morality of law.” This Article contends that Hart never offered a clear response. Fuller’s claim supposes that observance of the principles of legality is both fundamental to law and inherently moral. In different writings, Hart seems variously to affirm and to deny that legality is a necessary criterion for the existence of law. Likewise, he sometimes suggests and elsewhere scorns the idea that legality has moral significance. This Article proposes that Hart’s apparent inconsistency might actually reflect the complexity of the terms. Some degree of legality might be a prerequisite of law, while some failures of legality might not condemn it. Principles of legality might have contingent rather than inherent moral value, might have moral value that is severable from their legal value, or might have both positive and negative moral effect. The Article argues, furthermore, that even the conclusion Hart strains to avoid— that legality inevitably links morality and law—is compatible with Hart’s positivism and opens a promising field for positivist jurisprudence.