This paper will examine the way in which libraries are stewards of collections—the ways in which they help maintain the integrity of a collection, preserve its existence, and ensure that it is in some way made accessible to researchers. Throughout this paper, reference will be made to a variety of collections in libraries where the author has worked. These references are made not necessarily to illustrate best (or indeed worst) practices, but to help describe the difficulties that libraries sometimes encounter as stewards of collections. This paper poses several questions to librarians and to scholars, chief amongst them, ‘when is a collection no longer a collection?’ The collections dealt with in this paper are primarily book collections.