The Intergovernmental Panel on Climate Change (IPCC) was jointly established by the World Meteorological Organization and the United Nations Environment Programme (UNEP) in 1988. The purpose of Working Group 1 (WG1) of the IPCC is to assess available information on the science of climate change and to provide policy-relevant but not policy-prescriptive assessments of interest to policymakers, scientists, and the public. IPCC is currently beginning preparation of its fourth comprehensive assessment report (AR4) of the state of understanding of climate change, to be completed in 2007. During 2003, two scientific scoping meetings were held to identify the topics and structure for the new assessment, and the outline of the report was presented to and approved by Governments. The author teams were assembled in 2004, and the process of writing the assessment will begin in September, 2004. In this talk, the key scientific results of the scoping process will be highlighted, including emerging questions that are among the topics to be assessed. The comments, questions, and interests expressed by Governments in the course of the scoping process will also be described. Finally, a personal perspective on the pitfalls, pleasures, and challenges of scientific assessment will be discussed.