Tibetan Buddhism (also referred to as Tibeto-Mongol Buddhism, Indo-Tibetan Buddhism, Lamaism, Lamaistic Buddhism, Himalayan Buddhism, and Northern Buddhism) is a form of Buddhism practiced in Tibet and Mongolia. It also has a sizable number of adherents in the areas surrounding the Himalayas, including the Indian regions of Ladakh, Sikkim, and Arunachal Pradesh, as well as Bhutan and Nepal. Smaller groups of practitioners can be found in Central Asia, Xinjiang, Inner Mongolia, and some regions of Russia, such as Tuva, Buryatia, and Kalmykia.

Tibetan Buddhism evolved as a form of Mahāyāna Buddhism stemming from the latest stages of Indian Buddhism (which included many Vajrayāna elements). It thus preserves many Indian Buddhist tantric practices of the post-Gupta early medieval period (500 to 1200 CE), along with numerous native Tibetan developments. In the pre-modern era, Tibetan Buddhism spread outside of Tibet primarily due to the influence of the Mongol Yuan dynasty (1271–1368), founded by Kublai Khan, which had ruled China, Mongolia, and parts of Siberia. In the Modern era, Tibetan Buddhism has spread outside of Asia because of the efforts of the Tibetan diaspora (1959 onwards). As the Dalai Lama escaped to India, the Indian subcontinent is also known for its renaissance of Tibetan Buddhism monasteries, including the rebuilding of the three major monasteries of the Gelug tradition.

Apart from classical Mahāyāna Buddhist practices like the six perfections, Tibetan Buddhism also includes tantric practices, such as deity yoga and the Six Dharmas of Naropa, as well as methods that are seen as transcending tantra, like Dzogchen. Its main goal is Buddhahood. The main language of scriptural study in this tradition is classical Tibetan.

Tibetan Buddhism has four major schools, namely Nyingma (8th century), Kagyu (11th century), Sakya (1073), and Gelug (1409). The Jonang is a smaller school that exists, and the Rimé movement (19th century), meaning "no sides", is a more recent non-sectarian movement that attempts to preserve and understand all the different traditions. The predominant spiritual tradition in Tibet before the introduction of Buddhism was Bon, which has been strongly influenced by Tibetan Buddhism (particularly the Nyingma school).

While each of the four major schools is independent and has its own monastic institutions and leaders, they are closely related and intersect with common contact and dialogue.