The Cornish people or Cornish are an ethnic group native to, or associated with Cornwall and a recognised national minority in the United Kingdom, which can trace its roots to the Brittonic Celtic ancient Britons who inhabited Great Britain from somewhere between the 11th and 7th centuries BC and inhabited Britain at the time of the Roman conquest. Many in Cornwall today continue to assert a distinct identity separate from or in addition to English or British identities. Cornish identity has also been adopted by some migrants into Cornwall, as well as by emigrant and descendant communities from Cornwall, the latter sometimes referred to as the Cornish diaspora. Although not included as a tick-box option in the UK census, the numbers of those writing in a Cornish ethnic and national identity are officially recognised and recorded.

Cornish is a Southwestern Brittonic language of the Celtic language family. Along with Welsh and Breton, Cornish is descended from the Common Brittonic language spoken throughout much of Great Britain before the English language came to dominate. For centuries, until it was pushed westwards by English, it was the main language of Cornwall, maintaining close links with its sister language Breton, with which it was mutually intelligible, perhaps even as long as Cornish continued to be spoken as a vernacular. Cornish continued to function as a common community language in parts of Cornwall until the mid 18th century, and there is some evidence for traditional speakers of the language persisting into the 19th century.