The Thar Desert (Rajasthani: थार मरुधर, Hindi:थार मरुस्थल, Urdu (Urdu: تھر صحرا also known as the Great Indian Desert) is a large, arid region in the northwestern part of the Indian subcontinent and forms a natural boundary running along the border between India and Pakistan. With an area of more than 200,000 km² (77,000 sq mi), it is the world's 9th largest subtropical desert.

It lies mostly in the Indian State of Rajasthan, and extends into the northern portion of Haryana and Punjab states and into southern Gujarat state. In Pakistan, the desert covers eastern Sindh province and the southeastern portion of Pakistan's Punjab province. The Cholistan Desert adjoins the Thar desert spreading into Pakistani Punjab province.

In India the Thar Desert (also known as the Great Indian Desert) extends from the Sutlej River, surrounded by the Aravalli Ranges on the east, on the south by the salt marsh known as the Great 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, about 3/5th of the total geographical area of the State.
In Pakistan, the desert covers eastern Sindh and the southeastern portion of Punjab, Pakistan. The Tharparkar District is one of the major parts of the desert area. Tharparkar consists of two words: Thar means ‘desert’ while Parkar stands for ‘the other side’.