Doon Valley, situated in the Indian states of Uttarakhand, Himachal Pradesh and Haryana, is long and wide valley in the Shivalik Hills of Lesser Himalayas. The valley is also known as "Dun" valley; the word Doon or Dun means valley. Doon Valley is situated between the Outer Himalayas and Lesser Himalayas, which is locally known as the Mussoorie Range. It is encompassed on all sides by mountains, with northern range running from Kalsi in the west to Muni Ki Reti in the east with Mussoorie at the centre and southern range running at south from Paonta Sahib in the west to Haridwar in the east. The valley also forms a watershed between Yamuna and Ganges rivers.

Ecology of Doon Valley
Doon Valley has a rich ecology with over 500 species of birds within the region including Mussoorie Hills and Rajaji National Park. This region along with its surrounding areas is also botanically rich. Several rivers and streams flow through this valley and they have their sources either in Mussoorie Hills or Shivalik Hills; the local rivers finally flow into Yamuna or Ganges rivers. There are some local protected areas around the Doon Valley, which are Rajaji National Park, Asan Barrage Conservation Reserve, Jhilmil Jheel Conservation Reserve etc.