Woodcut attributed to Albrecht Dürer.
Incunabula, Latin for 'swaddling clothes,' is the term used for books printed in the earliest period of printing with movable type, or, in other words, from the time of Gutenberg (ca. 1450) into the early 16th-century. The oldest, a book on virtues by Guillelmus Paraldus, was published 'not after 1475.' For more details see Incunabula in the Andover-Harvard Theological Library and also the work A Catalogue of the Fifteenth-century Printed Books in the Harvard University Library by James E. Walsh, available in the reference collection.