A Comprehensive Ocean-Atmosphere Data Set (COADS) was developed as a cooperative project to compile global weather observations from merchant ships since 1854 into a compact and usable data set. The project involved the National Oceanic and Atmospheric Administration (NOAA), the National Science Foundation's National Center for Atmospheric Research (NCAR), and other institutions. COADS includes 70 million marine reports from 1854–1979, processed into monthly summaries for each year, using 2° latitude × 2° longitude boxes. These summaries include 14 statistics for eight observed variables and 11 derived variables. The data set is continuously updated, with an update through 1986 planned for completion by early 1988. The development of COADS involved collecting and processing various data sources, including historical logbooks, ship weather reports, and other data sets. The data were converted into a uniform format, with quality controls applied to identify suspect data and duplicates. The data were then sorted and merged into a serial-input stream, with new global numbering systems for 10° and 2° boxes. Data quality control included checks for climatological extremes, consistency, and code legality, with flags used to mark suspect observations. Trimming was used to remove outliers, and the data were further processed into 19 variables and 14 statistics for each year-month-2° box. COADS includes a wide range of data products, such as sea-surface temperature, wind stress, and other climate variables. The data set has been used for various studies, including climate change detection and analysis. However, the data contain known inhomogeneities, such as biases in sea-surface temperature measurements, variations in wind reporting, and issues with ship identification and data location. These problems are addressed through additional processing and calibration using land-based data. COADS is used by over 50 institutions worldwide, including the NOAA Climate Analysis Center, the Canadian Climate Centre, and the Tropical Ocean Global Atmosphere (TOGA) Programme. The data set is continuously updated, with future updates planned to include data from the 1913–1919 period and other sparse data years. The data are available from NCAR and NCDC, with additional details provided in the Appendix. The project has been supported by funding from ERL, NCAR, and NCDC, with additional support from the Equatorial Pacific Ocean Climate Studies (EPOCS) program.A Comprehensive Ocean-Atmosphere Data Set (COADS) was developed as a cooperative project to compile global weather observations from merchant ships since 1854 into a compact and usable data set. The project involved the National Oceanic and Atmospheric Administration (NOAA), the National Science Foundation's National Center for Atmospheric Research (NCAR), and other institutions. COADS includes 70 million marine reports from 1854–1979, processed into monthly summaries for each year, using 2° latitude × 2° longitude boxes. These summaries include 14 statistics for eight observed variables and 11 derived variables. The data set is continuously updated, with an update through 1986 planned for completion by early 1988. The development of COADS involved collecting and processing various data sources, including historical logbooks, ship weather reports, and other data sets. The data were converted into a uniform format, with quality controls applied to identify suspect data and duplicates. The data were then sorted and merged into a serial-input stream, with new global numbering systems for 10° and 2° boxes. Data quality control included checks for climatological extremes, consistency, and code legality, with flags used to mark suspect observations. Trimming was used to remove outliers, and the data were further processed into 19 variables and 14 statistics for each year-month-2° box. COADS includes a wide range of data products, such as sea-surface temperature, wind stress, and other climate variables. The data set has been used for various studies, including climate change detection and analysis. However, the data contain known inhomogeneities, such as biases in sea-surface temperature measurements, variations in wind reporting, and issues with ship identification and data location. These problems are addressed through additional processing and calibration using land-based data. COADS is used by over 50 institutions worldwide, including the NOAA Climate Analysis Center, the Canadian Climate Centre, and the Tropical Ocean Global Atmosphere (TOGA) Programme. The data set is continuously updated, with future updates planned to include data from the 1913–1919 period and other sparse data years. The data are available from NCAR and NCDC, with additional details provided in the Appendix. The project has been supported by funding from ERL, NCAR, and NCDC, with additional support from the Equatorial Pacific Ocean Climate Studies (EPOCS) program.