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.