The Global Climate Observing System (GCOS) prepared its first assessment of the Adequacy of the Global Climate Observing System for the 4th session of the Conference of the Parties (COP-4) of the UN Framework Convention on Climate Change in 1998. This report investigated the common assumption "that there are more than enough observations being collected to meet these [the Convention's] needs, especially given all the recent improvements in observational technologies. In practice, available observations often have major deficiencies with respect to climate needs." The 5th session of the COP invited all Parties to provide detailed reports on systematic observation in accordance with the UNFCCC reporting guidelines on global climate observing systems. This decision also requested that a process for synthesising and analysing the information in these reports by developed. In addition, the GCOS Steering Committee (SC) requested that this process be extended to prepare a second assessment of the adequacy of the global climate observing systems. The goal will be to determine what progress has been made since the first report in defining and implementing climate observing networks and systems and to assess how well current systems and planned improvements will meet the needs of the Convention. The assessment will involve international experts in analysing the adequacy of the current global climate observing systems and will utilize the national reports to COP and other information available from national, regional and international agencies including the research community. The assessment will also address new developments and emerging opportunities such as the increasing capabilities shown by satellite systems to provide long-term, calibrated climate observations and new techniques for integrating global in situ and satellite observations. The paper will discuss the planning and process for the assessment, including the involvement of the scientific community. The assessment is to be a soundly based scientific report with political credibility.