Policies to develop and deploy CCS as a tool for climate change mitigation should consider the key differences between three classes of CCS projects: carbon-positive, near carbon-neutral and potentially carbon-negative. In class 1 are projects that are 'carbon positive' since they capture CO2 from the production of fossil hydrocarbon fuels and there is no guarantee that the CO2 generated when these are used will be captured and stored. Class 1 CCS might be treated as a condition of the 'licence to operate' for hydrocarbon production projects that emit large amounts of CO2, and be distinguished from other classes of CCS projects in any incentive framework. In the event of serious global action on climate change, it seems likely that class 1 CCS would be employed to minimise fossil fuel supply chain CO 2 emissions, but in addition all fossil fuels would need to be used with class 2, near carbon neutral, CCS, so that the vast majority of fossil carbon is captured and stored and the main products are decarbonised energy vectors such as electricity, hydrogen and heat. Class 2 CCS projects are generally more expensive than class 1 projects and require more novel technologies, so they are unlikely to be widely deployed at present without specific incentives, an analogous situation to that for many renewable generation technologies. Carbon negative class 3 projects, where biomass use and CCS are combined, or where CO2 is captured directly from the air, could also be important since they have the potential to achieve a net reduction in atmospheric CO2 concentrations, as well as to offset residual emissions from other classes of CCS.