The Canterbury Tales are written in which historical form of English?

The Canterbury Tales are written in Middle English.

Geoffrey Chaucer composed the work mainly between about 1387 and 1400, using a London dialect of late Middle English. This was the language of England after Old English had evolved through substantial Scandinavian and French influence, but before the later changes that produced Modern English.

The Tales presents a group of pilgrims travelling from London to Canterbury to visit the shrine of Saint Thomas Becket. They agree to tell stories during the journey, creating a frame narrative that lets Chaucer portray people from different occupations and social classes.

Modern readers often recognize individual words but miss the historical pronunciation and grammar. Chaucer's final e was frequently pronounced, and the Great Vowel Shift had not yet transformed English vowels. The work is therefore usually read in translation or with notes, even though it remains one of the central achievements of English literature.