The Book of the Duchess is a 1,334-line poem, the earliest of Chaucer's major poems. It exists in several manuscripts of varying accuracy, and for the last one hundred years (beginning with W. W. Skeat in the 1890s) it has been the task of editors to piece together an authoritative edition. It is commonly held by literary scholars that Chaucer wrote The Book of the Duchess in octosyllabic rhyming couplets. Copyists' errors and changes to the language have distorted this pattern, but it still can be discerned.
This is an example of a "dream poem" (or "dream-vision" or "dream allegory"), a mode of narrative common in Chaucer's day for English and Continental poets. The dream or vision experienced in the mind of the narrator of the poem (for they were often voiced in the first person) allowed a certain kind of message or theme to be communicated in a highly stylized manner. Often the dream is about a kind of wish-fulfillment, or the elevating or honoring (The Book of the Duchess is in fact an elegy) of something that would not be possible in the course of a realistic telling of a story. It also gives the poet ample space and scope to play with allegories and metaphors of all kinds.
It is generally, though not entirely, agreed by scholars that The Book of the Duchess is an elegy for Blanche, Duchess of Lancaster, who died in 1368 or 1369 of plague. Blanche was the first wife of John of Gaunt, Duke of Lancaster (son of King Endward III of England and, after his death, father of King Henry IV). However, there is some confusion about the date of the creation of the poem--and how long after the death of Blanche it occurred. Chaucer was not prone to commenting or mentioning the events of his time, and if indeed it is an elegy for a real person it is couched in allegorical form.
This poem was heavily influenced by the style of the French "love poets," the makers of courtly love poems such as Guillaume de Lorris, Jean de Meun, Froissart, and Machaut. In fact, Chaucer lifted entire lines from Machaut's Jugement dou Roy de Behaingne. The form of elegy and much of the imagery are borrowed from him.
Two other poems of Chaucer, The House of Fame (unfinished) and The Parliament of Fowls, are more of Chaucer's dream-visions. The House of Fame is also written in octosyllabic couplets, and it is similar in style to the works of the French poets who also influenced The Book of the Duchess. The House of Fame was written around 1380, while The Book of the Duchess was composed some ten years (or more) earlier. The House of Fame shares some of the features of the earlier poem, including the type of narrator, discussions of dream theory, and a concern with all aspects of courtly and romantic love.
The Parliament of Fowls, composed in rime royal, was written sometime between the two above poems. It might be one of the very first celebrations of Saint Valentine's Day ever recorded. Like the other poems, the narrator is guided through a vision supposed to help him learn wisdom in love. It is concerned with folktale: on the feast of Saint Valentine, all the birds assemble before Dame Nature to choose their mates. At the end the dreamer wakes but continues his quest for wisdom.