The Kola Superdeep Borehole (KSDB) is a Russian-funded project to drill into the Earth's crust. Begun in 1970 on the Kola Peninsula, a number of boreholes were made from a central branch. The deepest, SG-3, was completed in 1994, creating a hole 12.262 kilometers (seven miles) deep, the deepest hole ever made by humans.

The project has been a site of extensive geophysical studies. The stated areas of study were the deep structure of the Baltic Shield; seismic discontinuities and the thermal regime in the Earth's crust; the physical and chemical composition of the deep crust and the transition from upper to lower crust; lithospheric geophysics; and to create and develop technologies for deep geophysical study.

The project was first proposed in 1962 and was assigned to the Interdepartmental Scientific Council for the Study of the Earth's Interior and Superdeep Drilling (Междуведомственный научный совет по изучении недрам земли и сверхглубокое бурение). The drill site was chosen in 1965 in north-west Soviet Union, 10 km north of the town of Zapolyarniy .

The site is currently controlled by the State Scientific Enterprise on Superdeep Drilling and Complex Investigations in the Earth's Interior (GNPP Nedra) as the Deep Geolaboratory. The currently active deepest bore is SG-5, it is 8578 m deep and 214 mm in diameter.