The Thar Desert (also known as the Great Indian Desert) is a hot desert that forms a significant portion of western India. Spread over four states in IndiaPunjab, Haryana, Rajasthan, and Gujarat it covers an area of 208,110km (80,350mile). The desert continues into Pakistan as the Cholistan Desert. Most of the Thar Desert is situated in Rajasthan, covering 61% of its geographic area. Most of the desert is rocky, with a small part of the extreme west of the desert being sandy.

The origin of the Thar Desert is uncertain. Some geologists consider it to be 4,000 to 10,000 years old, whereas others state that aridity began in this region much earlier. The area is characterised by extreme temperatures of above 45C (113F) in summer to below freezing in winters. Rainfall is precarious and erratic, ranging from below 120mm (4.72inches) in the extreme west to 375mm (14.75inches) eastward. The lack of rainfall is mainly due to the unique position of the desert with respect to the Aravalli range. The desert lies in the rain shadow area of the Bay of Bengal arm of the southwest monsoon. The parallel nature of the range to the Arabian Sea arm also means that the desert does not receive much rainfall.

The soils of the arid region are generally sandy to sandy-loam in texture. The consistency and depth vary according to the topographical features. The low-lying loams are heavier and may have a hard pan of clay, calcium carbonate or gypsum. Due to the low population density, the effect of the population on the environment is relatively less compared to the rest of India.