Gangtok (Sikkimese: [ɡaŋt̪ʰòk]) is the capital and the most populous city of the Indian state of Sikkim. The seat of eponymous district, Gangtok is in the eastern Himalayan range, at an elevation of 1,650 m (5,410 ft). The city's population of 100,000 consists of the three Sikkimese ethnicities: the Bhutias, Lepchas, Indian Gorkhas as well as plainsmen from other states of India. Within the higher peaks of the Himalayas and with a year-round mild temperate climate, Gangtok is at the centre of Sikkim's tourism industry.

Gangtok rose to prominence as a popular Buddhist pilgrimage site after the construction of the Enchey Monastery in 1840. In 1894, the ruling Sikkimese Chogyal, Thutob Namgyal, transferred the capital to Gangtok. In the early 20th century, Gangtok became a major stopover on the trade route between Lhasa in Tibet and cities such as Kolkata (then Calcutta) in British India. After India won its independence from the British Empire in 1947, Sikkim chose to remain an independent monarchy, with Gangtok as its capital. After Sikkim's merger with India in 1975, Gangtok continued as the state capital.

The precise meaning of the name "Gangtok" is unclear, though most agree that the meaning is "hill top", in Tibetan: སྒང་ཏོག་་, the Wylie transliteration being Sgang Tog.

Like the rest of Sikkim, not much is known about the early history of Gangtok. The earliest records date from the construction of the hermitic Gangtok monastery in 1716. Gangtok remained a small hamlet until the construction of the Enchey Monastery in 1840 made it a pilgrimage centre. It became the capital of what was left of Sikkim after its English conquest in the mid-19th century in response to a hostage crisis. After the defeat of the Tibetans by the British, Gangtok became a major stopover in the trade between Tibet and British India at the end of the 19th century. Most of the roads and the telegraph in the area were built during this time.

In 1894, Thutob Namgyal, the Sikkimese monarch under British rule, shifted the capital from Tumlong to Gangtok, increasing the city's importance. A new grand palace along with other state buildings was built in the new capital. Following India's independence in 1947, Sikkim became a nation-state with Gangtok as its capital. Sikkim came under the suzerainty of India, with the condition that it would retain its independence, by the treaty signed between the Chogyal and the then Indian Prime Minister Jawaharlal Nehru. This pact gave the Indian government control of external affairs of Sikkim. Trade between India and Tibet flourished through the Nathula and Jelepla passes, benefiting Gangtok. Trade declined with the Chinese crackdown in Tibet in 1959 and the passes were sealed after the Sino-Indian War in 1962. The Nathula pass was finally opened to limited trade in 2006, fuelling hopes of an economic boom.

In 1975, after years of political uncertainty and struggle, including riots, the monarchy was abrogated and Sikkim became India's twenty-second state, with Gangtok as its capital after a referendum.

Gangtok has witnessed annual landslides, resulting in loss of life and damage to property. The largest disaster occurred in June 1997, when 38 people were killed and hundreds of buildings were destroyed.

Gangtok is located at 27°19′57″N 88°36′50″E / 27.3325°N 88.6140°E / 27.3325; 88.6140 (coordinates of Gangtok head post office). It is in the lower Himalayas at an elevation of 1,650 m (5,410 ft). The town is on the side of a hill, with "The Ridge", a promenade with the Raj Bhawan, the governor's residence, at one end and the palace, at an altitude of about 1,800 m (5,900 ft), at the other. The city is flanked east and west by two streams, Roro Chu and Ranikhola. These two rivers divide the natural drainage into two parts, eastern and western. Both streams meet the Ranipul and flow south as the Ranikhola before joining the Teesta at Singtam. Most roads are steep, with the buildings built on compacted ground alongside them.