Carbon offsetting is the act of mitigating("offsetting") greenhouse gasemissions. A well-known example is the purchase of carbon offsets to compensate for the greenhouse gas emissions caused by personal air travel.

The concept of paying for emission reductions to take place elsewhere instead of reducing one's own emissions is known from the related concept of

A wide variety of offset methods are in use. While tree planting was initially a mainstay of carbon offsetting, renewable energy, energy conservation and methane capture offsets have become popular. Purchase and withdrawal of emissions trading credits also occurs, which creates a connection between the voluntary and regulated carbon markets.

Carbon offsetting as part of a "carbon neutral" lifestyle has gained some appeal and momentum mainly among consumers in western countries who have become aware and concerned about the potentially negative environmental effects of energy-intensive lifestyles and economies. The Kyoto Protocol has sanctioned offsets as a way for governments and private companies to earn carbon credits which can be traded on a marketplace. The protocol established the Clean Development Mechanism (CDM), which validates and measures projects to ensure they produce authentic benefits and are genuinely "additional" activities that would not otherwise have been undertaken. Organisations that have difficulty meeting their emissions quota are able to offset by buying CDM-approved Certified Emissions Reductions. The CDM encourages projects that involve, for example, sustainable power generation, changes in land use, and forestry, although not all trading countries allow their companies to buy all types of credit.

The commercial system has contributed to the increasing popularity of voluntary offsets among private individuals, companies, and organizations. Offsets may be cheaper or more convenient alternatives to reducing one's own fossil-fuel consumption. However, some critics object to carbon offsets, and many have questioned the benefits of certain types of offsets, such as tree planting.