The Joint Air-Sea Interaction (JASIN) 78 Project Data Set comprises a variety of measurements including upper air and near surface meteorology, and physical oceanography. Meteorological data include air temperature, pressure, humidity and wind, while oceanographic data include temperature, salinity, currents, wave spectra and short-term wave statistics. The data were collected in the North Rockall Trough, an area of deep water (1000m - 2000m) several hundred kilometres off the west coast of Scotland. The experiment lasted for 2 months from mid-July to mid-September 1978 and comprised 2 intensive observational phases preceded by a preparatory test period. Data were collected using a variety of instrumentation, with meteorological data being provided by radiosondes, tethered balloons, and ship- and aircraft-mounted sensors. Hydrographic data were collected via shipboard deployment of conductivity-temperature-depth (CTD) sensor packages (both standard and yoyo profiles), towed thermistor chains, ship-mounted wave recorders and moored temperature and current meters. The JASIN Project was designed to study the interaction of the atmospheric and oceanic boundary layers with the large scale motions of the sea and air. The multiplicity of processes sampled necessitated a large experiment and involved more than 50 teams of investigators from nine countries. The data are held at the British Oceanographic Data Centre and many series are available via BODC's online data delivery portal.