Troy Book is a Middle English poem by John Lydgate relating the history of Troy from its foundation through to the end of the Trojan war. It is in five books, comprising 30,117 lines in ten-syllable couplets. The poem's major source is Guido delle Colonne's Historia destructionis Troiae.
Troy Book was Lydgate's first full-scale work. It was commissioned from Lydgate by the Prince of Wales (later Henry V), who wanted a poem that would show the English language to be as fit for a grand theme as the other major literary languages,
Ywriten as wel in oure langage
As in Latyn and in Frensche it is.
Lydgate tells us that he began writing the poem at four o'clock in the afternoon of Monday, 31 October 1412; he completed it in 1420.
It has been argued that Lydgate intended Troy Book as an attempt to outdo Chaucer's Trojan romance Troilus and Criseyde, and certainly the frequent recurrence of tributes to Chaucer's excellence as a poet is a notable feature of the poem. The poem emphasizes the disastrous results of political discord and militarism, and also presents the conventional medieval themes of the power of Fortune to influence earthly affairs and the vanity of worldly things.
Troy Book survives in 23 manuscripts, testifying to the popularity of the poem during the 15th century. It was printed first by Richard Pynson in 1513, and second by Thomas Marshe in 1555. A modernized version sometimes attributed to Thomas Heywood, called The Life and Death of Hector, appeared in 1614. Troy Book exercised an influence on Robert Henryson, Thomas Kyd, and Christopher Marlowe, and was one of Shakespeare's sources for Troilus and Cressida.