The Himalayas or Himalaya (from Sanskrit hima (snow) + ālaya (dwelling), literally meaning "abode of snow") is a mountain range in the Indian subcontinent which separates the Indo-Gangetic Plain from the Tibetan Plateau. This range is home to nine of the ten highest peaks on Earth, including the highest above sea level, Mount Everest. The Himalayas have profoundly shaped the cultures of South Asia. Many Himalayan peaks are sacred in both Buddhism and Hinduism.

The Himalayas are bordered on the north by the Tibetan Plateau, on the south by the Indo-Gangetic Plain, on the northwest by the Karakoram and Hindu Kush ranges, and on the east by the Indian states of Sikkim, the Darjeeling district of West Bengal,Assam, Arunachal Pradesh and Manipur. The Hindu Kush, Karakoram and Himalayas form together the "Hindu Kush Himalayan Region" (HKH). The western anchor of the Himalayas—Nanga Parbat—lies just south of the northernmost bend of theIndus River, while the eastern anchor—Namcha Barwa—is situated just west of the great bend of the Yarlung Tsangpo River. The Himalayas span five countries: India, Nepal, Bhutan, China (Tibet), and Pakistan, with the first three countries having sovereignty over most of the range.

Mt. Kangchenjunga or Kangchendzonga, as seen from Tiger Hill, Darjeeling is India's tallest peak.

Lifted by the collision of the Indian tectonic plate with the Eurasian Plate,[6] the Himalayan range runs northwest to southeast in a 2,400-kilometre (1,500 mi) long arc. The range varies in width from 400 kilometres (250 mi) in the west to 150 kilometres (93 mi) in the east. Besides the Greater Himalayas, there are several parallel lower ranges. The southernmost of these, located along the northern edge of the Indian plains and reaching about a thousand meters in altitude, are called the Sivalik Hills. Further north is a higher range, reaching two to three thousand meters, known as the Lower Himalayan Range.

Three of the world's major rivers—the Indus, the Ganges and the Brahmaputra—arise in the Himalayas. While the Indus and the Brahmaputra rise near Mount Kailash in Tibet, the Ganges rises in the Indian state of Uttarakhand. Their combined drainage basin is home to some 600 million people.

The flora and fauna of the Himalayas vary with climate, rainfall, altitude, and soils. The climate ranges from tropical at the base of the mountains to permanent ice and snow at the highest elevations. The amount of yearly rainfall increases from west to east along the southern front of the range. This diversity of altitude, rainfall and soil conditions combined with the very high snow line supports a variety of distinct plant and animal communities. The extremes of high altitude (low atmospheric pressure) combined with extreme cold favor extremo phileorganisms.

The unique floral and faunal wealth of the Himalayas is undergoing structural and compositional changes due to climate change. The increase in temperature is shifting various species to higher elevations. The oak forest is being invaded by pine forests in the Garhwal Himalayan region. There are reports of early flowering and fruiting in some tree species, especially rhododendron, apple and box myrtle. The highest known tree species in the Himalayas is Juniperus tibeticalocated at 4,900 metres (16,080 ft) in Southeastern Tibet.

The Himalayan range is one of the youngest mountain ranges on the planet and consists mostly of uplifted sedimentary and metamorphic rock. According to the modern theory of plate tectonics, its formation is a result of a continental collision or orogeny along the convergent boundary between the Indo-Australian Plate and the Eurasian Plate. The Arakan Yoma highlands in Myanmar and the Andaman and Nicobar Islands in the Bay of Bengal were also formed as a result of this collision.

During the Upper Cretaceous, about 70 million years ago, the north-moving Indo-Australian plate (which has subsequently broken into theIndian Plate and the Australian plate) was moving at about 15 cm per year. About 50 million years ago this fast moving Indo-Australian plate had completely closed the Tethys Ocean, the existence of which has been determined by sedimentary rocks settled on the ocean floor, and the volcanoes that fringed its edges. Since both plates were composed of low density continental crust, they were thrust faultedand folded into mountain ranges rather than subducting into the mantle along an oceanic trench.[6] An often-cited fact used to illustrate this process is that the summit of Mount Everest is made of marine limestone from this ancient ocean.

Today, the Indian plate continues to be driven horizontally below the Tibetan Plateau, which forces the plateau to continue to move upwards. The Indian plate is still moving at 67 mm per year, and over the next 10 million years it will travel about 1,500 km into Asia. About 20 mm per year of the India-Asia convergence is absorbed by thrusting along the Himalaya southern front. This leads to the Himalayas rising by about 5 mm per year, making them geologically active. The movement of the Indian plate into the Asian plate also makes this region seismically active, leading to earthquakes from time to time.

During the last ice age, there was a connected ice stream of glaciers between Kangchenjunga in the east and Nanga Parbat in the west. In the west, the glaciers joined with the ice stream network in the Karakoram, and in the north, joined with the former Tibetan inland ice. To the south, outflow glaciers came to an end below an elevation of 1,000–2,000 metres (3,300–6,600 ft). While the current valley glaciers of the Himalaya reach at most 20 to 32 kilometres (12 to 20 mi) in length, several of the main valley glaciers were 60 to 112 kilometres (37 to 70 mi) long during the ice age. The glacier snowline (the altitude where accumulation and ablation of a glacier are balanced) was about 1,400–1,660 metres (4,590–5,450 ft) lower than it is today. Thus, the climate was at least 7.0 to 8.3 °C (12.6 to 14.9 °F) colder than it is today.