Kangchenjunga is the third-highest mountain in the world. Its summit lies at 8,586 m (28,169 ft) in a section of the Himalayas, the Kangchenjunga Himal, which is bounded in the west by the Tamur River, in the north by the Lhonak River and Jongsang La, and in the east by the Teesta River. It lies in the border region between Koshi Province of Nepal and Sikkim state of India, with the West and Kangbachen peaks located in Nepal's Taplejung District and the Main, Central and South peaks directly on the border.

Until 1852, Kangchenjunga was assumed to be the highest mountain in the world. However, precise calculations and meticulous measurements by the Great Trigonometrical Survey of India in 1849 showed that Mount Everest, known as Peak XV at the time, is actually higher. After allowing for further verification of all calculations, it was officially announced in 1856 that Kangchenjunga is the third-highest mountain in the world.

Kangchenjunga is a sacred mountain in Nepal and Sikkim and was first climbed on 25 May 1955 by Joe Brown and George Band, who were part of the 1955 British Kangchenjunga expedition. They stopped just short of the true summit, keeping a promise given to Tashi Namgyal, the Chogyal of the Kingdom of Sikkim, that the top of the mountain would remain inviolate. The Indian side of the mountain is off limits to climbers. In 2016, the adjoining Khangchendzonga National Park was declared a UNESCO World Heritage Site.

Kangchenjunga is the official spelling adopted by Douglas Freshfield, Alexander Mitchell Kellas and the Royal Geographical Society, and provides the most accurate English rendition of the Tibetan pronunciation. Freshfield referred to the spelling used by the Indian Government since the late 19th century. Alternative spellings include Kanchenjunga, Khangchendzonga and Kangchendzönga.

The brothers Hermann, Adolf and Robert Schlagintweit explained the local name 'Kanchinjínga', meaning "the five treasures of the high snow", as originating from the Tibetan words "gangs" pronounced [kaŋ], meaning snow and ice; "chen", pronounced [tɕen] meaning great; "mdzod", meaning treasure; and "lnga", meaning five. The local Lhopo people believe that the treasures are hidden but reveal themselves to the devout when the world is in peril; the treasures comprise salt, gold, turquoise and precious stones, sacred scriptures, invincible armor or ammunition, grain and medicine.

The Kangchenjunga Himal section of the Himalayas lies both in Nepal and India and encompasses 16 peaks over 7,000 m (23,000 ft). In the north, it is limited by the Lhonak Chu, Goma Chu and Jongsang La, and in the east by the Teesta River. The western limit runs from the Jongsang La down the Gingsang and Kangchenjunga glaciers and the rivers of Ghunsa and Tamur. It lies in the border region between Koshi Province of Nepal and Sikkim state of India, with the peaks West and Kangbachen in Nepal's Taplejung District, and three of the five peaks, namely Main, Central and South, directly on the border.

Kanchenjunga rises about 20 km (12 mi) south of the general alignment of the Great Himalayan range, about 125 km (78 mi) east-southeast of Mount Everest in a straight line. South of the southern face of Kanchenjunga runs the 3,000–3,500 m (9,800–11,500 ft) high Singalila Ridge that separates Sikkim from Nepal and northern West Bengal. Until 1852, Kangchenjunga was assumed to be the highest mountain in the world, but calculations and measurements by the Great Trigonometrical Survey of India in 1849 showed that Mount Everest, known as Peak XV at the time, is actually higher. After allowing for further verification of all calculations, it was officially announced in 1856 that Kangchenjunga was the third-highest mountain after Everest and K2 of Karakoram.

Kangchenjunga and its satellite peaks form a huge mountain massif. The massif's five highest peaks are listed in the table at the end of this section.