This report reviews technological options for mitigating carbon dioxide (CO2) emissions. The options analyzed include efficiency  improvements, renewable energies, clean fossil and zero-carbon technologies, carbon sequestration and disposal, enhancement of natural carbon sinks (halting deforestation, afforestation, and other sink enhancement options), and geo-engineering measures to compensate for increases in CO2 concentrations. Reduction potentials, costs, and the relative contribution of individual options, as well as their limiting factors and possible timing of introduction and diffusion are discussed. The study concludes with a discussion of methodological issues and trade-offs and constraints for implementation strategies to mitigate anthropogenic sources of change in the global carbon cycle.