Long a sovereign state, Sikkim became a protectorate of India in 1950 and a state in 1975. Because of its location, it has a political and strategic importance out of proportion to its size.

Sikkim is a basin surrounded on three sides by precipitous mountain walls. There is little lowland, and the variation in relief is extreme. Within 50 miles (80 kilometres) the land rises from an elevation of 750 feet in the Tīsta River valley to 28,208 feet (8,598 metres) at Kānchenjunga, India's highest peak and the world's third highest mountain. The Singālila Range separates Sikkim from Nepal in the west, while the Dongkya Range forms the border with China to the east. Several passes across this range afford easy access to the Chumbi valley in Tibet and beyond to Lhasa, imparting considerable strategic and political value to the region.

About two-thirds of Sikkim consists of perpetually snow-covered mountains, dominated by the Kānchenjunga massif. The Sikkimese have traditionally viewed the mountain as both a god and the abode of gods. The legendary Abominable Snowman, or yeti, called Nee-gued in Sikkim, is believed to roam its slopes. Other major peaks—all above 23,000 feet—include Tent, Kabru, and Pauhunri.

The Sikkim basin is drained by the Tīsta River and its tributaries, such as the Rangīt, Rongni Chu, Talung, and Lachung, which have cut deep valleys into the mountains. Originating in a glacier near the Tibetan border, the Tīsta River descends steeply, dropping about 15,700 feet to Rongphu (Rangpo), where it has cut a gorge through the Dārjiling Ridge (7,000–8,000 feet) before emerging onto the Gangetic Plain. Hydroelectric projects on Sikkim's rivers provide power to Gangtok, Rongphu, Singtām, and Mangan.

Sikkim exhibits a variety of climatic types, from almost tropical conditions in the south to the severe mountain climates in the north. Depending on altitude and exposure, annual precipitation varies from 50 to 200 inches (1,270 to 5,080 millimetres), most occurring during the months of the southwest monsoon (May through October). The heavy rains and snows often trigger destructive landslides and avalanches.

About one-third of Sikkim is forested. Sal, pandanus, palms, bamboos, ferns, and orchids are common in the subtropical forests found below about 5,000 feet. In the temperate forests (5,000 to 13,000 feet), oak, laurel, maple, chestnut, magnolia, alder, birch, rhododendron, fir, hemlock, and spruce predominate. Alpine tundra replaces forest at the higher elevations.

Sikkim has a rich and varied animal life, including the black bear, brown bear, panda, numerous species of deer, wild goats, sheep, goral, and the Tibetan antelope; the tiger, leopard, and lesser cats are also found. Birdlife includes pheasant, partridges, quail, eagles, barbets, Himalayan cuckoos, Tibetan black crows, and minivets.

Three-quarters of Sikkim's population is Nepalese in origin, speaking Nepālī (Gorkhalī) dialects and mostly Hindu in religion and culture. The Bhutiā (Bhutia), Lepchā, and Limbu are significant minorities; they speak Tibeto-Burman dialects and practice Mahāyāna Buddhism and the pre-Buddhist Bon religion. Migrants from India since 1985 have added to the Hindu population, and there are also a small number of Christians and Muslims.

The population is mostly rural, living in scattered hamlets and villages. Gangtok, with fewer than 30,000 people, is Sikkim's largest settlement; other towns, in descending order of population, include Singtām, Rongphu, Jorthang, Nayabazar, Mangan, Gyalshing, and Namchi.

Copper, lead, zinc, coal, graphite, and limestone are among the minerals found in the state, though not all are commercially exploited. Forest resources and hydroelectric potential are considerable. Sikkim, however, is predominantly agricultural. Corn (maize), rice, buckwheat, wheat, and barley are produced in terraced fields along the valley flanks. Beans, ginger, potatoes, vegetables, fruits, and tea also are grown. Sikkim is one of the world's main producers of cardamom.

Livestock includes cattle, pigs, sheep, goats, and poultry. Cattle and buffalo are limited mainly to the subtropical humid belt, while yaks and sheep are herded in the higher elevations in the north.

Until the early 1970s, Sikkim had only cottage industries—producing handwoven textiles, carpets, and blankets—as well as traditional handicrafts, such as embroidery, scroll paintings, and wood carving. There are now a number of small-scale industries, including a flour mill, a tannery, a watch assembly unit, a distillery, a fruit preservation plant, and a tea processing factory.

Roads, though not extensive, are the primary mode of travel. Ropeways have also been provided at many points. The capital of Gangtok is nearly 75 miles from the nearest airport at Bāghdogra and 70 miles from the railhead at Shiliguri, both in West Bengal.

Sikkim's head of state is a governor, appointed by the president of India and aided by the chief minister and Council of Ministers. Seats in the elected Legislative Assembly (Vidhān Sabhā) are equally apportioned between the Nepalese and the minority Lepchā and Bhutiā populations. One Lepchā-Bhutiā seat is reserved for the nominee of the lamas (Buddhist religious leaders), and one seat of the Nepalese group is reserved for the representative of the Scheduled Castes.

The state is divided into four districts—North, East, South, and West—with headquarters at Mangan, Gangtok, Namchi, and Gyalshing, respectively. Within each district, local headmen serve as liaisons between the people and the district administration. Pañcāyats (village councils) administer the villages and implement welfare programs.

Primary and secondary education is free in the state. A government-subsidized degree college located in Gangtok is affiliated with North Bengal University at Dārjiling, West Bengal.

Sikkim's cultural life, though showing strong Tibetan influences, retains a character derived from the various tribes of Sikkim and their pre-Buddhist customs. The most important festival of the year is the two-day Phanglhapsol festival in August or September, in which masked dancers perform in honour of Kānchenjunga, the presiding deity. The Namgyal Institute of Tibetology has one of the largest collection of Tibetan books in the world. Many monasteries are repositories of artistic treasures, including wall paintings, thang-kas (religious paintings mounted on brocade), and bronze images.

Little is known of Sikkim's history prior to the 17th century. The state's name is derived from the Limbu words su him, meaning “new house.” The Lepchā were early inhabitants of the region, apparently assimilating the Naong, Chang, Mon, and other tribes. The Bhutia began entering the area from Tibet in the 14th century. When the kingdom of Sikkim was established in 1642, Phuntsog Namgyal, the first chogyal (temporal and spiritual king), came from this community. The Namgyal dynasty ruled Sikkim until 1975.

Sikkim fought a series of territorial wars with both Bhutan and Nepal beginning in the mid-18th century, and Nepal subsequently came to occupy parts of western Sikkim and the submontane Tarai. It was during this period that the largest migration of Nepalese to Sikkim began. In 1816 these territories were restored to Sikkim by the British in return for its support during the Anglo-Nepalese War (1814–16), but by 1817 Sikkim had become a de facto protectorate of Britain.

The British (British Empire) East India Company obtained Dārjiling from Sikkim in 1835. Incidents between the British and Sikkim led to the annexation in 1849 of the submontane regions and the subsequent military defeat of Sikkim, culminating in the Anglo-Sikkimese Treaty of 1861. The treaty established Sikkim as a princely state under British paramountcy (though leaving the issue of sovereignty undefined), and the British were given rights of free trade and of road making through Sikkim to Tibet. In 1890 an agreement was concluded between the British and the Tibetans that defined the border between Sikkim and Tibet. Tibet also acknowledged the special relationship of British India with the kingdom of Sikkim. A British political officer was subsequently appointed to assist the chogyal in the administration of Sikkim's domestic and foreign affairs and, in effect, became the virtual ruler of the state.

In 1950, three years after India attained independence from Britain, a treaty was signed between Sikkim and India that made Sikkim an Indian protectorate. India assumed responsibility for the external relations, defense, and strategic communications of Sikkim.

After 1947 political parties began to be formed in Sikkim for the first time. Among their aims were the abolition of feudalism, the establishment of popularly elected government, and accession of Sikkim to India—all demands resisted by the chogyal and his supporters. The terms of the 1950 Indo-Sikkimese treaty, however, included increased popular participation in government, and five general elections based on adult suffrage were held between 1952 and 1974. In the last of these elections, two rival parties merged to form the Sikkim Congress, which swept the polls. The party launched a campaign to obtain greater political liberties and rights that the chogyal attempted to suppress. With the situation getting out of control, the chogyal asked the government of India to take over the administration. India prepared a constitution for Sikkim that was approved by its national assembly in 1974. In a 1975 special referendum, more than 97 percent of the electorate voted for the merger of Sikkim with India. Sikkim became the 22nd state of the Indian Union on May 15, 1975.