A carbon credit (or otherwise referred to as a carbon offset) is equivalent to 1 ton of CO2 equivalent (i.e. could be SF6 or NOx but they are all converted to CO2 equivalents). Under the Kyoto Protocol, each nation (and in turn each company) is allocated a certain amount of credits allowing them the right to pollute into the atmosphere as measured against a base year. The natural by-product of business creates pollution and everyone recognizes that cannot be stopped immediately. The Kyoto Protocol, reduces the amount of credits allotted to countries/companies over time (through 2012) so that there is a goal of reducing the overall level of greenhouse gases emitted (despite the fact that plant and equipment is getting older and GDP is expanding). Businesses and countries are permitted to trade these credits between each other as the UN does not care if one party is a large offender and the other party is less of an offender since it is simply the global level of pollutants that matters. As such, these credits have economic value as a tradeable commodity. This is the so-called Cap and Trade model. Credits are able to be created by ANYONE who does an environmentally friendly project that reduces man-made greenhouse gases and gets their methodology approved by the United Nations. Examples of which are planting forests, farming methane gas from landfills, patching Gas pipelines from leaking, capping SF6, etc. The emissions that would otherwise be generated into the atmosphere are measured and 1 credit is issued for each ton of CO2 otherwise saved. These credits are now tradeable to companies in Kyoto countries (the compliance markets) and they are tradeable in non-Kyoto countries such as the US under the Voluntary Market (VERs). The net effect is that there is a Cap and a reduction of the overall level of greenhouse gas emissions mandated under the Kyoto Protocol through 2012 (which will get renewed). Entrepreneurs/developers can create credits that have economic value by engaging in environmentally friendly projects (this is usually very profitable as companies would often rather purchase pollution rights rather than upgrade plant and equipment or reduce business). Net, net, greenhouse gas emissions are reduced under the capital markets cap and trade approach. Those that do the projects get paid (and often rich) for doing these projects, companies view them as a cost of doing business which essentially amounts to a pollution tax and individuals (or companies) buy them in the Voluntary market to do their part to reduce their greenhouse gas emissions or for the positive public relations effect of branding their businesses carbon neutral or green. Make sense?