What language did Chaucer write?

Geoffrey Chaucer wrote in Middle English. Middle English is a period in the history of the English language that lasted from the end of the 11th century to the end of the 15th century. It is a transitional period between Old English and Modern English, and it was during this time that the language underwent significant changes in pronunciation, grammar, and vocabulary. Chaucer's works, such as The Canterbury Tales, are considered to be some of the greatest works of literature in English, and they have played an important role in shaping the development of the English language.