The U.S. Climate Change Science Program is in the process of producing 21 draft assessments that investigate changes in the Earth's climate and related systems. These assessments are designed to inform decisionmakers about the scientific underpinnings of a range of environmental issues, such as models of past climate conditions. This National Research Council book reviews one of these assessments, Synthesis and Assessment Product 1.3 "Reanalyses of Historical Climate Data for Key Atmospheric Features: Implications for Attribution of Causes of Observed Change." The committee commends the authors for clearly stating their goals and their intended audience and for their fidelity in following the prospectus. However, the current draft needs revision to better link reanalysis and attribution. In addition, the document needs to better explain how reanalysis fits into climate science and include a general description of how climate science is done and how the models, observations, and theories are related to the ultimate goal of reanalysis, especially for the benefit of non-specialists.