Environmental laws often mandate specific environmental outcomes and require agencies to adopt plans designed to achieve those outcomes. But because of pervasive uncertainties, agencies are often unsure if their plans will succeed. Decisionmakers therefore must decide how to balance risks of plan failure against the costs of more cautious regulatory approaches. This Article explores and evaluates legal responses to these dilemmas. I find that environmental statutes and regulations use a patchwork of measures to manage these planning uncertainties. Decisions about planning uncertainty are frequently made on an ad hoc, nontransparent basis, and plans with low success odds are common. That approach is problematic, for it impedes public participation, increases vulnerability to decisionmaking biases, and contributes to regulatory dysfunction. I therefore propose procedural and substantive reforms designed to improve transparency and to reduce the frequency of plan failure.