This is the first detailed analysis of the fate of Lucretius' De rerum natura from its beginnings in the 50s BC down to the creation of our earliest extant manuscripts during the Carolingian age. A detailed investigation of the knowledge of Lucretius' poem among writers throughout the Roman, and subsequently the medieval, worlds allows fresh insight into the work's readership and reception, and an assessment of the value of the indirect tradition for editing the poem. The first extended analysis of the 170+ subject headings (capitula) that intersperse the text reveals the close engagement of Roman readers. A fresh inspection and assignation of marginal hands in the poem's most important manuscript provides new evidence about the work of Carolingian correctors and the basis for a new Lucretian stemma codicum. Further clarification of the interrelationship of Renaissance manuscripts of Lucretius gives additional evidence of the poem's reception in fifteenth-century Italy.