This report provides an estimation of the funds that will be needed to build carbon sink capacity in 25 rain forest nations to enable them to participate in the Reduced Emissions from Deforestation and Forest Degradation mechanism, an instrument proposed under the UN Convention on Climate Change that rewards countries for avoiding the removal or degradation of forests. This paper was commissioned by the Office of Climate Change as background work to its report "Climate Change: Financing Global Forests" (the Eliasch Review).