As far as we know, Chaucer hardly wrote any poetry at all in the first half of his life. All of his best-known works were written in his thirties or later, when he was more established in his career and probably had more freedom to write. In 1374, Edward III awarded Chaucer a lucrative, cushy job as Comptroller of Customs for the Port of London. Chaucer was smart enough to hold on to the gig for the next twelve years. During this time, he wrote most of his major works.
It is impossible to determine the exact year that Chaucer wrote or published most of his works. Scholars have been able to work out a time period in which most of the works were published based on the historical record. For example, the Duchess of Lancaster died in 1369, and a ledger shows that Chaucer was paid for her elegy in 1374, so the Book of the Duchess must have been written sometime during those five years. In the late 1370s, Chaucer wrote Anelida and Arcite, a poem based on Boccaccio's Italian epic Teseida (Chaucer also bases the Knight's tale in The Canterbury Tales on Teseida). It was about the Armenian queen Anelida, who was courted by the Grecian Arcite. Many of Chaucer's poems after that were dream visions, a genre in which the narrator relates what he has perceived in a dream state. From 1379 to 1380, Chaucer wrote The House of Fame, a 2,000-line dream vision. Shortly thereafter, he composed Parlement of Foules (also written as Parlement of Fowles), a 700-line dream vision in which the narrator travels to Venus' temple.
In 1380, according to legal records, Chaucer was accused of the raptus - a term that can mean rape or kidnapping - of a woman named Cecilia Chaumpaigne. Though Chaumpaigne later exonerated Chaucer of the crime, the details of the incident are unknown. It appears to have been settled quickly, since the incident is never mentioned again in any records associated with Chaucer. Rape was a serious charge in medieval England, but Chaucer's career did not seem to have suffered from the accusation. It is one of the mysteries of his biography.
Sometime between 1382 and 1388, Chaucer composed his first truly great work in Middle English. The epic poem Troilus and Criseyde was a Middle English take on the Greek classic tragedy of two doomed lovers. (The story is a favorite of great English poets; Shakespeare tackled it in his play Troilus and Cressida.) Unlike most of Chaucer's works - including The Canterbury Tales - Chaucer actually finished Troilus and Criseyde. Though it's not as well known as The Canterbury Tales, many Chaucer aficionados believe that it is his best work. He followed it with another dream vision, The Legend of Good Women.
Sometime in the late 1380s, Chaucer began his final poetic work. He spent ten years on the project, finishing only a quarter of what he had originally planned to write. The result was by far his most famous poem. We're talking, of course, about The Canterbury Tales. For all of its venerable reputation, The Canterbury Tales is basically a 600-year-old B.S. contest. The Tales focused on a group of 31 pilgrims making their way to Canterbury Cathedral in order to visit the shrine of Thomas Becket, the martyred archbishop assassinated by King Henry II's adherents. To pass the time, they have a contest to see who can tell the best story. The winner gets a free dinner.
The Canterbury Tales is both a work of poetry and anthropology. Chaucer's tale is like a cross-sectional view into medieval English life. Each pilgrim is identified by his or her profession - knight, nun, miller, student - and the stereotypes and characteristics that fourteenth century English people associated with differing social class. It was by far the most substantial work ever written in Middle English. It was also about as popular as a book could get in the era before the printing press was invented. With the Gutenberg press still 50 years away from its invention, copies of the poem had to be made by hand (!). Dozens of copies of The Canterbury Tales still survive from Chaucer's era, evidence that the book was exceptionally popular.