The Global Sea Level Observing System (GLOSS) 'Delayed-mode' Data Assembly Centre at the British Oceanographic Data Centre (BODC) quality controls and archives high frequency (i.e. hourly or more frequent) global sea level data and any ancillary measurements (e.g. temperature, wind speed/direction, atmospheric pressure) that are included with the data. The tide gauges are situated on most coastlines, and data cover the Arctic to the Antarctic, and the Atlantic, Indian and Pacific oceans. The main component of GLOSS is the 'Global Core Network' (GCN) of 290 sea level stations around the world for long term climate change and oceanographic sea level monitoring. The Core Network is designed to provide an approximately evenly-distributed sampling. The GLOSS Long Term Trends (LTT) set of gauge sites (some, but not all, of which are in the GCN) are used for monitoring long term trends and accelerations in global sea level. The GLOSS altimeter calibration (ALT) set consists mostly of island stations, and provides a facility for mission intercalibrations. A GLOSS ocean circulation (OC) set, including in particular gauge pairs at straits and in polar area, complements altimetric coverage of the open deep ocean. Data exist from the mid 1800s up to the present day, with particularly long records from Newlyn, U.K.; Brest, France; Prince Rupert, Canada and Honolulu, San Diego and San Francisco, U.S.A.; Sea level has been measured by a variety of different instruments with the historical data mainly coming from mechanical float gauges. More recent technologies include acoustic, pressure, and radar instruments. GLOSS aims at the establishment of high quality global and regional sea level networks to create long‐term sea level records. These records, as well as being used in climate studies (sea level rise), are also used in oceanography (ocean currents, tides, surges), geodesy (national datum), geophysics and geology (coastal land movements) as well as various other disciplines. The programme became known as GLOSS as it provides data for deriving the 'Global Level of the Sea Surface'. GLOSS is an international programme conducted under the auspices of the Joint Technical Commission for Oceanography and Marine Meteorology (JCOMM) of the World Meteorological Organisation (WMO) and the Intergovernmental Oceanographic Commission (IOC). Data are collected by local agencies such as port authorities, universities and navies and sent to or downloaded by the data centre.