This presentation will discuss the development of a series of specialized observational data sets for the World Climate Research Programme (WCRP) Coordinated Enhanced Observing Period. CEOP is composed of a number of global WCRP research programmes [i.e. Global Energy and Water Cycle Experiment (GEWEX), Climate Variability and Predictability (CLIVAR), and Climate and Cryosphere (CliC)]. Each one of the GEWEX Continental Scale Experiments selected a number of well instrumented reference sites in various climatic regions of the world (36 in total) to support CEOP research activities. These reference sites provide observations of surface meteorology, radiation, fluxes, soils, and atmospheric profiles in a variety of spatial and temporal resolutions in different formats. The University Corporation for Atmospheric Research/Joint Office for Science Support (UCAR/JOSS) takes these disparate data and conducts a consistent processing and quality assurance methodology leading to the development of a data set in a consistent format and temporal resolution. This presentation will discuss the current status of the CEOP EOP-3 (1 October 2002 to 30 September 2003) data processing, quality assurance, and data archival and distribution as well as plans for the remaining CEOP reference site data sets.