The dataset includes a wide range of physical, chemical and biological oceanographic parameters. Physical hydrographic measurements include temperature, salinity, optical backscatter, current velocities and turbulence, while biogeochemical measurements in the water column include dissolved oxygen, organic carbon and nitrogen, and nutrients. Biogeochemical parameters were also measured in sediment cores, while phytoplankton and zooplankton data were also collected. The marine data were supplemented by meteorological measurements including temperature, pressure, irradiance and wind. The experimental phase of the project was undertaken in the North Sea between 1998 and 1999, and data were collected at two contrasting sites: Northern North Sea (NNS, 59deg 20.0E, 1deg 00.0E) and Southern North Sea (SNS, 52deg 15.0N, 4deg 17.0E). At both locations measurements were concentrated at a central position with additional measurements being made to estimate horizontal gradients. Moored instruments were deployed at NNS from September - November 1998 and at SNS from March - May 1999. Each experiment was supported by intensive measurement series made from oceanographic ships and involving turbulence dissipation profiler, conductivity-temperature-depth (CTD) profilers, particle size profilers, optical profilers, benthic sampling and water bottle sampling. PROVESS is an interdisciplinary study of the vertical fluxes of properties through the water column and the surface and bottom boundary layers with the aim of improving understanding and quantification of vertical exchange processes in the water column. Scientists from 18 institutions distributed in 8 European countries participated in the fieldwork and modelling parts of the programme and was co-ordinated by John Howarth of the Proudman Oceanographic Laboratory. The British Oceanographic Data Centre (BODC) is responsible for assembling the data collected during the project into a comprehensive data set. The data has been organised onto a CD-ROM product available through BODC.