Carbon credits represent the right to emit one tonne of carbon dioxide or its equivalent. They are part of national and international efforts to mitigate greenhouse gas emissions. Under emissions trading programs, emissions are capped and markets are used to allocate allowances among regulated groups. The goal is to use market mechanisms to encourage low-emissions approaches. Credits can also be voluntarily purchased to offset carbon footprints. Quality and prices vary depending on whether credits are from compliance markets or secondary markets.