Udiana (also: Uḍḍiyāna, Uḍḍāyāna, Udyāna or 'Oḍḍiyāna'), a small region in early medieval India, is ascribed importance in the development and dissemination of Vajrayāna Buddhism. Tibetan Buddhist traditions view it as a Beyul (Tibetan: སྦས་ཡུལ, Wylie: sbas-yul), a legendary heavenly place inaccessible to ordinary mortals. Padmasambhava, the eighth-century Buddhist master who was instrumental in the introduction of Buddhism to Tibet, was believed to have been born in Oddiyana. The Dzogchen Siddha Garab Dorje is likewise attributed to this region.

It is ascribed importance in the development and dissemination of Vajrayāna Buddhism. The region was also an important place for the practice of Śaivite Hinduism. It is seen as the homeland of the Mahārtha (aka Krama Kalikula) lineage of Śaiva Tantra. The first Mahārtha Siddha, Jñānanetra Nātha (ज्ञाननेत्र नाथ), is said to have awakened and taught in this country. It was also called as “the paradise of the Ḍākinīs”.

Many Western scholars have identified it as the Swat Valley in what is now Khyber Pakhtunkhwa in Pakistan. Laurence Waddell, Sylvain Lévi, Giuseppe Tucci, and Prabodh Chandra Bagchi have shown that the Tibetan name Urgyan and the Chinese name Wutch'ang correspond to Uddiyana which is identical with the modern-day Swat Valley. Alexis Sanderson revisited the issue of the location, taking note of the various far-flung locations that have been identified with Oddiyana at different times and by different sources. He came to the conclusion, drawn from his careful examination of a variety of old textual citations, that it was located near Kashmir, accepting the modern-day Swat as the probable epicentre of a historical Oddiyana.

Udyāna (Sanskrit "garden, orchard") is sometimes reported as being located north of Peshawar along the Swat River; it was regarded as the furthest part of northern ancient India during the time of Faxian. The 8th century Korean monk Hye Cho wrote in his Memoir of the travel to the five Indian regions that after visiting Gandhara, he went directly north, entered the mountains and after travelling for three days, arrived in Udyana (locally called Oddiyana), a mountainous Buddhist region. From Udyana, he travelled northeast for fifteen days and reached Chitral. Faxian stated that the food and clothing worn by those in Udyana were similar to those residing in the Indo-Gangetic Plain.

The area is said to have supported some 500 viharas of the Sthavira nikāya, at which traveling monks were provided lodgings and food for three days. It was said to contain a Buddha footprint, a rock on which he dried his clothes, and a locale where he converted a nāga. It is said that two schools derived from the Sthavira nikāya, the Dharmaguptaka and Kāśyapīya, were established in this area. Both of these schools had proto-Mahayana doctrines.

While the 6th to 8th century Kabul Ganesh offers a memorial inscription, to Turk Shahis king Khingala of Oddiyana.

The following Hindu Shahis are believed to belong to the Uḍi/Oḍi tribe, namely the people of Oddiyana whose rulers were already known at the time of the Kushan Empire (3rd century CE) and are recorded as early as the 4th century BCE.

An alternate theory places its location in what is now the modern Indian state of Odisha, through a case founded upon "literary, archeological and iconographic evidence". Scholars championing this location contend that the name Oḍḍiyāna derives from the Dravidian Oṭṭiyan, denoting a native or indigenous person of Oḍra ("Odisha") or from Oṭṭiyam, Telugu for Oḍra. Oḍḍiyāna is also the Middle Indic form of Udyāna "garden," the name by which Xuanzang knew the region around Odisha.