The presence of advertisements in books, whether as publicity for other publications from the same house, or for products of quite another sort, from the late Eighteenth century onwards (but examples are known and have been documented from previous eras), should never be underestimated by the bibliographer. In the first place such advertising is often the first ‘bibliography’ received by some titles. It should always be noted whether the advertisement forms part of the edition, i.e. it is printed on the same sheets, or whether it forms a separate physical unit, perhaps on a differently-coloured paper, in which case it can identify a separate ‘binding-up’ (cfr. below). On the bibliographical exploitation of such evidence, see W.B. Todd, ‘On the Use of Advertisements in Bibliographical Studies’, The Library, 5th s., 8 (1953), pp. 174-187.