The EISCAT (European Incoherent Scatter) Scientific Association is an international research organisation operating three incoherent scatter radar systems, at 931 MHz, 224 MHz and 500 MHz, in Northern Scandinavia. It is funded and operated by research councils of Norway, Sweden, Finland, Japan, China and the United Kingdom (collectively, the EISCAT Associates). Germany (until 2011) and France (until 2005) are earlier EISCAT Associates.

EISCAT studies the interaction between the Sun and the Earth as revealed by disturbances in the magnetosphere and the ionised parts of the atmosphere (these interactions also give rise to the spectacular aurora, or Northern Lights). The radars are operated in both Common and Special Programme modes, depending on the particular research objective, and Special Programme time is accounted and distributed between the Associates according to rules which are published from time to time.

One EISCAT transmitter site consisting of a UHF system and a VHF system is located close to the city of Tromsø, in Norway, and additional receiver stations are located in Sodankylä, Finland, and Kiruna, Sweden. The EISCAT Headquarters are also located in Kiruna. In 1996 the EISCAT Scientific Association constructed a second incoherent scatter radar facility, the EISCAT Svalbard Radar (ESR), near Longyearbyen on the island of Spitsbergen, far to the North of the Norwegian mainland.

In addition to the incoherent scatter radars, EISCAT also operates an Ionospheric Heater facility at Ramfjordmoen to support various active plasma physics experiments in the high latitude ionosphere, as well as Dynasondes at Ramfjordmoen and on Svalbard.

Raw datum are matrices of correlation functions.

Approximately half of EISCAT operations consist of Common Programmes. The Common Programme (or CP) experiments currently comprise six generic modes, each of which should be run a few times per year. The purpose of the Common Programme is to enable EISCAT to obtain, over a period of years, a high-quality synoptic database of homogeneous observations, suitable for statistical studies and for the identification of seasonal, annual and solar cycle effects.

Approximately half of EISCAT operations are devoted to Special Programmes. These are experiments carried out by individual scientists or collaborating groups, usually in connection with highly specialised research topics. Data from Special Programmes are reserved for the proposing experimenters for the first year after the data have been taken. Thereafter, their status becomes the same as Common Programme data. Because Special Programmes are intended for the specialised study of certain events or phenomena, the experiments tend to comprise non-standard modes, different from the normal Common Programmes, though this is not always the case.

Approximately half of EISCAT operations are devoted to Special Programmes. These are experiments carried out by individual scientists or collaborating groups, usually in connection with highly specialised research topics. Data from Special Programmes are reserved for the proposing experimenters for the first year after the data have been taken. Thereafter, their status becomes the same as Common Programme data. Because Special Programmes are intended for the specialised study of certain events or phenomena, the experiments tend to comprise non-standard modes, different from the normal Common Programmes, though this is not always the case.