Editors' Summary: Emissions trading has emerged as the major policy instrument to address climate change, as evidenced by programs and proposals in Australia, Europe, the United States, and elsewhere. A host of choices need to be made to design and implement a greenhouse gas emissions trading program, choices that are important both to the performance of the program and to the many private firms and groups that are affected. In this Article, David Harrison Jr., Per Klevnas, Albert L. Nichols, and Daniel Radov investigate these alternatives. They explain that private firms and sectors need to understand how their costs and revenues might be affected--including differences depending upon various policy alternatives--and to determine how to take advantage of the flexibility provided by emissions trading. The development of a carbon market as well as the other market effects of a climate change program also will affect key decisions such as the development of new capacity or the retirement of existing plants and equipment. Understanding these influences will help firms and sectors to respond effectively and, in the process, allow the trading programs to achieve goals of meeting key climate change objectives at lowest cost to society.