The high costs for the US economy of mitigating climate change have been cited by the Bush administration as one of the reasons for rejecting US ratification of the Kyoto Protocol. A range of cost estimates are assessed in the IPCC's third report (2001), but they are hedged with so many qualifications that it is not easy to reach useful conclusions. This paper organises. some of the quantitative information on costs of greenhouse gas mitigation for the US published before the US rejection of Kyoto. The aim is to put them in a wider context, e.g., allowing for non-climate benefits, and to draw conclusions that are robust in the face of the uncertainties. Important lessons can be drawn for how costs can be reduced in any future international commitment by the US to reduce emissions. Provided policies are expected, gradual and well designed (e.g., through auctioned Annex I tradable permits with revenues used to reduce burdensome tax rates) the net costs for the US of mitigation are likely to be insignificant, that is within the range +/-1% of GDP.