He is most known for his unfinished work, The Canterbury Tales, which is regarded as one of the greatest works of poetry in English

It is a fact that he is most known for his unfinished work, The Canterbury Tales, which is regarded as one of the greatest works of poetry in English. The Canterbury Tales is a collection of twenty-four stories that runs to over 17,000 lines written in Middle English by Geoffrey Chaucer between 1387 and 1400. It is widely regarded as Chaucer's magnum opus. The tales (mostly written in verse, although some are in prose) are presented as part of a story-telling contest by a group of pilgrims as they travel together from London to Canterbury to visit the shrine of Saint Thomas Becket at Canterbury Cathedral. The prize for this contest is a free meal at the Tabard Inn at Southwark on their return.

It has been suggested that the greatest contribution of The Canterbury Tales to English literature was the popularisation of the English vernacular in mainstream literature, as opposed to French, Italian, or Latin. English had, however, been used as a literary language centuries before Chaucer's time, and several of Chaucer's contemporaries, John Gower, William Langland, the Pearl Poet, and Julian of Norwich, also wrote major literary works in English. It is unclear to what extent Chaucer was seminal in this evolution of literary preference.

The Canterbury Tales is generally thought to have been incomplete at the end of Chaucer's life. In the General Prologue, some 30 pilgrims are introduced. According to the Prologue, Chaucer's intention was to write four stories from the perspective of each pilgrim, two each on the way to and from their ultimate destination, St. Thomas Becket's shrine making for a total of about 120 stories. Although perhaps incomplete, The Canterbury Tales is revered as one of the most important works in English literature.