The Cornish language revival (Cornish: dasserghyans Kernewek, lit. ''resurrection of Cornish'') is an ongoing process to revive the use of the Cornish language of Cornwall, England. The Cornish language's disappearance began to hasten during the 13th century, but its decline began with the spread of Old English in the 5th and 6th centuries. The last reported person to have full knowledge of a traditional form of Cornish, John Davey, died in 1891. The revival movement started in the late 19th century as a result of antiquarian and academic interest in the language, which was already extinct, and also as a result of the Celtic revival movement. In 2009, UNESCO changed its classification of Cornish from "extinct" to "critically endangered", seen as a milestone for the revival of the language.

During the 19th century, the Cornish language was the subject of antiquarian interest and a number of lectures were given on the subject and pamphlets on it were published. In 1904, the Celtic language scholar and Cornish cultural activist Henry Jenner published A Handbook of the Cornish Language. The publication of this book is often considered to be the start of the current revival movement. The spelling in this book was based on that used when Cornish was last a community language in the 18th century.

The first project to codify Cornish spelling and provide a regular orthography for the revived language was that of Robert Morton Nance who outlined his work in Cornish for All in 1929. Unlike the Late Cornish-based work of Jenner, Nance's orthography, called Unified Cornish (Kernewek Unys), was based mainly on the Middle Cornish of the 14th and 15th centuries. Nance believed that this period represented a high point for Cornish literature. As well as presenting a standardised spelling system, Nance also extended the attested vocabulary with forms based largely on Breton and Welsh, and published a dictionary of Unified Cornish in 1938. Nance's purist approach favoured older 'Celtic' forms rather than the historically more recent forms deriving from Middle and Early Modern English.

Nance's work became the basis of revived Cornish and his orthography was the only one in use for most of the 20th century. However, as the focus shifted from written to spoken Cornish, Nance's stiff, archaic formulation of the language seemed less suitable for a spoken revival. Also, Nance's phonology lacked some distinctions which later research showed must have existed in traditional Cornish. Unified Cornish is still in use by some speakers who, while acknowledging its shortcomings, feel it has served well for the first decades of the revival.

Its IETF language tag is kw-uccor.

In 1986, in response to dissatisfaction with Unified Cornish, Ken George undertook a study of the sounds of Cornish and devised a new orthography, Kernewek Kemmyn or Common Cornish, based on his research. Like Unified Cornish, Kernewek Kemmyn retained a Middle Cornish base but implemented an orthography that aspired to be as phonemic as possible. George argued that this much closer relationship between sounds and writing would make Cornish much easier to teach and learn.

In 1987, after one year of discussion, the Cornish Language Board agreed to adopt it. Its adoption by the Cornish Language Board caused a division in the Cornish language community, especially since people had been using Nance's old system for many years and were unfamiliar with the new one. While it was adopted by a majority of Cornish speakers (various estimates put it at around 55–80%), it was criticised by Nicholas Williams and Jon Mills for various reasons, as well as those who found its novel orthography too different from traditional Cornish spelling conventions.

Its IETF language tag is kw-kkcor.