This classroom game illustrates the strengths and weaknesses of various regulatory frameworks aimed at internalizing negative externalities from pollution. Specifically, the game divides students into three groups--a government regulatory agency and two polluting firms--and allows them to work through a system of uniform command-and-control regulation, a tradable emissions permit framework, and an emissions tax. Students observe how flexible, market-oriented regulatory frameworks can outperform inflexible command-and-control. More important, given the ongoing debate about how best to regulate carbon dioxide emissions, students also can observe how the introduction of abatement-cost uncertainty can cause one market-oriented solution to outperform another. (Contains 4 tables and 5 notes.)