Ground-based interferometric gravitational-wave search refers to the use of extremely large interferometers built on the ground to passively detect (or "observe") gravitational wave events from throughout the cosmos.[1] Most recorded gravitational wave observations have been made using this technique; the first detection, revealing the merger of two black holes, was made in 2015 by the LIGO sites.
As of 2024[update], major detectors are the two LIGO sites in the United States, Virgo in Italy and KAGRA in Japan, which are all part of the second generation of operational detectors. Developing projects include LIGO-India as part of the second generation, and the Einstein Telescope and Cosmic Explorer forming a third generation. Space-borne interferometers such as LISA are also planned, with a similar concept but targeting different kind of sources and using very different technologies.[1]: 40