The Thar Desert (Hindi: also known as the Great Indian Desert, is a large, arid region in the northwestern part of the Indian subcontinent. With an area of more than 200,000 sq. km., (140,000 sq. mi.) it is world's seventeenth largest desert. It lies mostly in the Indian state of Rajasthan, and extends into the southern portion of Haryana and Punjab states and into northern Gujarat state. In Pakistan, the desert covers eastern Sind province and the southeastern portion of Pakistan's Punjab province. The Cholistan Desert adjoins the Thar desert spreading into Pakistani Punjab province.

The Thar Desert is bounded on the northwest by the Sutlej River, on the east by the Aravalli Range, on the south by the salt marsh known as the Rann of Kutch (parts of which are sometimes included in the Thar), and on the west by the Indus River. Its boundary to the large thorny steppe to the north is ill-defined. Depending on what areas are included or excluded, the nominal size of the Thar can vary significantly.