Abstract: In recent years, the idea of “nondelegation canons” has gained currency in public law. The phrase nicely captures the aspiration that courts can use interpretive presumptions or clear statement rules—such as the federalism canons, the norm against retroactivity, and the presumption against extraterritoriality—to implement constitutional and other substantive or systemic values. The basic idea is that such canons allow effective enforcement of underenforced constitutional values by insisting that Congress speak clearly when it wishes to invade the specified values. In that way, such canons function very much like a nondelegation doctrine, forcing Congress to make its disfavored policies express in the statute. One of the asserted advantages of nondelegation canons is that they force Congress to take responsibility for important policy decisions without the judicial administrability problems that have dissuaded the Court from enforcing the nondelegation doctrine through judicial review. In conventional nondelegation cases, the Court has expressed anxiety about its own competence to judge when a statute is so vague or open-ended that it impermissibly transfers legislative power to an agency or court. With nondelegation canons, however, the Court feels comfortable simply giving the benefit of the doubt to interpretations that do not invade favored values. Using the presumption against preemption as an example, this Essay argues that nondelegation canons, in fact, present the same line-drawing problems as the traditional nondelegation doctrine. All such canons require courts to identify when an interpretive decision is properly attributed to a statute passed by Congress rather than to policymaking discretion exercised by an agency or court. Because all statutes embody some degree of ambiguity, deciding when a statute is clear enough to warrant such attribution involves the same kind of question of degree that makes the Court wary of the nondelegation doctrine as such.