The fundamental dataset consists of full water column temperature and salinity profiles, with discrete inorganic nutrient data added later on. Between 1975 and January 1996 there were usually multiple occupations, in a single year, of a section between the Scottish shelf and the Rockall Channel. Many of these occupations targeted only a selection of the 35 stations collectively recognised as the Ellett Line. Over the years various names were used to describe the hydrographic section (or components of it): The Rockall Section, The Anton Dohrn Seamount Section, The Shelf-Edge-Sound of Mull Section. These are collectively termed the Ellett Line, after the scientist David Ellett, who coordinated much of this early work. The Extended Ellett Line consisted of 58 identified stations between the North West coast of Scotland and Iceland, crossing the Scottish shelf, Rockall Channel and Iceland Basin. The Extended Ellett Line was occupied at least annually from 1996 to 2018. The water column profiles were collected using STDs/CTDs at recognised fixed stations along the section. The discrete inorganic nutrient data were obtained from water bottles fired at multiple depths on each profile, although these data are absent (or more limited) in the earlier stages of the time series. In 2018, the Extended Ellett Line became the Ellett Array. The Ellett Array consists of moorings, gliders and CTD sections in the Rockall Trough and Hatton-Rockall Basin. The overall Ellett Line/Extended Ellett Line/Ellett Array dataset is recognised as a key oceanographic time series. Several important water masses are captured within it – water masses that help drive ocean thermohaline circulation and consequently regulate climate on a global scale. The multi-decadal nature of the dataset provides a rare opportunity for scientists to monitor changing ocean circulation patterns. Ellett Line occupations were first carried out by the Scottish Marine Biological Association (SMBA), now the Scottish Association for Marine Science (SAMS). From 1996 there was a move to joint maintenance, with Southampton Oceanography Centre (SOC), now the National Oceanography Centre (NOC), sharing the responsibility with SAMS. Data collection as part of the Ellett Array is an ongoing activity. Some of the data are subject to a two-year embargo upon generation, after which they become available as part of this growing unrestricted data collection.