Presentation of a paper presented at the Collection Thinking Conference, Concordia University, June 12-14 2018. 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 to ensure that it is in some way made accessible to researchers. I’m going to talk about how libraries treat collections, and a little about why they do so. I will present four examples of collections that are held by libraries where I have worked, each of which fulfils a different definition of what a collection is and how it interacts with the larger library collection.