For decades, controversy has brewed over agency (ab)use of and (over)reliance on guidance documents. On one account, agencies turn to guidance in an end run around notice-and-comment requirements, producing de facto legislative rules without either public input or, at least in some cases, judicial scrutiny. On another, guidance documents are good government in action, a helpful and illuminating benefit. In Preambles as Guidance, Kevin Stack does not take sides in this debate. But he does helpfully remind us that there is one type of guidance that (a) is not subject to the standard critique and (b) is often not appreciated as guidance at all. This overlooked creature, hiding in plain sight, is the preamble that accompanies every final rule.