What is a cap-and-trade program and how does it work?

A cap-and-trade program is designed to reduce emissions of a pollutant by placing a limit (or cap) on the total amount of emissions. The cap is implemented through a system of allowances that can be traded to minimize costs to affected sources. Cap-and-trade programs for greenhouse gas emissions would increase the costs of using fossil fuels.
EIA’s Energy in Brief: What everyone should know about energy