IN the selection of incunabula - in the happy days when this was a fairly regular activity - the first and uppermost reason for acquisition was typographical. The British Library collection aims to represent the work of all printers who produced books in the fifteenth century, and to have samples of all types used by them. This collecting principle has now existed for a century. The astonishingly representative collection of incunabula had been brought together based on a multitude of tastes and preferences, not necessarily connected with the history of printing. In the foundation collections - Sloane, the Old Royal Library - incunabula were present for their textual interest. The Reverend C. M. Cracherode bequeathed in 1799 incunabula of the highest quality of illumination and general condition. The greatest influx came with the King's Library - where the spread of printing was certainly one of the spheres of interest - and the Grenville collection, with particular interest in vernacular literature, and for texts relating to travel and discovery. In spite of the very diverse motives which at one time or other drove collectors to acquire these books, once they were brought together in one collection (and augmented from the 1850s to 1870s with a large number of items, for the most part obtained very cheaply), they constituted a representation of book production in the fifteenth century which was unrivalled in any other institution.