Pāli is a middle Indo-Aryan dialect or prakrit.

It is most famous as the language in which the scriptures of Theravada Buddhism (also known as the Pāli Canon or in Pāli the Tipitaka) were written down in Sri Lanka in the first century BC.

Pāli has been written in a variety of scripts, from Brahmi, Devanagari and other Indic scripts through to a romanised (western) form devised by T. W. Rhys Davids of the Pali Text Society.

The word Pāli itself signifies "line" or "(canonical) text" and it is now classified as a literary language.

While it is uncertain whether Pāli was ever a spoken language in the sense of a language people use to communicate with each other, Pāli has long been a the language in which Theravada Buddhists chant. It is widely believed that Gotama Buddha spoke either in the vernacular Magadhi or some other middle Indo-Aryan vernacular which was the language of the people near Benares in North-East Central India (now Varanasi) where he resided and taught. Pāli was considered by early Buddhists to be linguistically similar to old Madaghi or even a direct continuation of that language. However, Madaghi is an Eastern Indian language whereas Pali most closely resembles Western Indian inscriptions.

Today Pāli is studied mainly to gain access to Buddhist scriptures, and is frequently chanted. The Pali Text Society, based in the United Kingdom, has since its founding in 1881 been a major force in promoting the study of Pāli by Western scholars. The society publishes these scriptures in romanised Pāli and most of them in English translation as well.

Many Pāli words come from Sanskrit with the original meaning slightly altered to accommodate the content of Buddhism. Other Pāli words come from places where Pāli was used (e.g. Sri Lankans adding Sinhalese words to Pāli.)

The Pāli vocabulary reflects the fact that Pāli is used principally to convey the teachings of the Buddha. Similar words in Sanskrit can have slightly different meanings than those of Pāli. For example, Buddhists do not believe things have an essential nature or eternal soul, so the literal meaning of the word "dhamma" (Sanskrit "dharma") is modified to reflect this.

The philosophy of Sanskrit and Pāli are opposites and reflect the division between Buddhism and the Brahmanical thought of the Middle Indic period. While Sanskrit words were thought to inhere as a part of the thing they described, Pāli words were thought to have only conventional significance.