A bhikkhuni (Pāli) or bhikṣuṇī (Sanskrit) is a fully ordained female Buddhist monastic. Male monastics are called bhikkhus. Both bhikkhunis and bhikkhus live by the vinaya. Bhikkhuni lineages enjoy a broad basis in Mahayana countries like Korea, Vietnam, China, and Taiwan.

According to Buddhist scriptures, the order of bhikkhunis was first created by the Buddha at the specific request of his foster-mother Mahapajapati Gotami, who became the first ordained bhikkhuni, relayed via his attendant Ananda (who also urged for the Buddha's acceptance of it). The bhikkhuni order spread to many countries.

For a country or nation to be considered as truly Buddhist, the majority of the nation must be Buddhist and include at least a fourfold assembly of bhikkhus, bhikkhunis, upasakas and, upasikas.

According to Theravada tradition, the bhikkhuni order of nuns came to be five years after the bhikkhu order of monks.

Buddhism is unique among Indian Religions in that Buddha, as founder of a spiritual tradition, explicitly states in canonical literature that a woman is as capable of nirvana (enlightenment) as a man, and can fully attain all four stages of enlightenment in the Dhamma and Vinaya of the Buddha Sasana. There is no equivalent, in other traditions, of the Therigatha or Apadanas which record the high levels of spiritual attainment by women.