The CCHDO provides access to standard, well-described datasets from reference-quality repeat hydrography expeditions. It curates high quality full water column Conductivity-Temperature-Depth (CTD), hydrographic, carbon and tracer data from over 2,500 cruises from ~30 countries. It is the official data center for CTD and water sample profile data from the Global Ocean Ship-Based Hydrographic Investigations Program (GO-SHIP), as well as for WOCE, US Hydro, and other high quality repeat hydrography lines (e.g. SOCCOM, HOT, BATS, WOCE, CARINA.)