EISCAT, the European Incoherent Scatter Scientific Association, is established to conduct research on the lower, middle and upper atmosphere and ionosphere using the incoherent scatter radar technique. We conduct ionospheric and atmospheric measurements with radars. This technique is the most powerful ground-based tool for these research applications. As an example we can observe effects of the aurora borealis or the northern lights. EISCAT is also being used as a coherent scatter radar for studying instabilities in the ionosphere, as well as for investigating the structure and dynamics of the middle atmosphere and as a diagnostic instrument in ionospheric modification experiments with the Heating facility, a combined ionospheric heating and short-wave radar facility. We operate in three countries: Finland, Norway and Sweden, and all our facilities are located north of the Arctic circle. We are associated with our radar antennas, that are located in Kiruna, Sweden; Sodankylä, Finland; Tromsø, Norway and in Longyearbyen, Svalbard. EISCAT is currently building a new system, EISCAT_3D, which will replace the current mainland radar systems. EISCAT_3D is a modern, multi-static, phased array radar system now being deployed at three locations in Finland, Norway, and Sweden. The build started in 2017 and the new system will be ready for use in 2023.