This Article discusses cap setting for a cap-and-trade program, a key problem in pending legislation addressing global climate disruption. While the literature often suggests that trading automatically solves the problems associated with Best Available Technology (BAT) regulation, regulators often use a BAT approach to setting caps for trading programs. This paper examines neglected normative and practical choices between BAT, cost-benefit, and effects-based cap setting in the trading context. It also shows that cap setting exercises can get bogged down in the same sort of lengthy administrative and judicial processes that delayed and weakened BAT regulation, and discusses ways of avoiding these problems in climate legislation.