This chapter offers a consideration of the magic lantern slide from a series of viewpoints giving overlapping ways of thinking about what it is as an artefact, how it works as a component of a narrative and performance medium, and its significances in historical and contemporary contexts of creative use. With illustrations from the Lucerna web resource, institutional and private collections, and the work of the Million Pictures research project, the chapter considers the physicality of slides as objects; their relative cultural (and financial) valuations; their various roles and motivations in the transference and concealment of knowledge; their relationships with other portions of the projection process; and some parallels between historic usage of slides and modern media practices, especially in the complex mixture of ‘authority’ and ‘freedom’ that determines their use and interpretation. Conventional approaches to what is sometimes called the ‘historical art of projection’ can be prone to dwell on one or two of these aspects, often with an emphasis on the visual content of the slide image or the physical nature of the artefact. However, to begin to understand the overall cultural impact of this largely lost medium we need to open out the discussion beyond its component parts and consider its possible uses, both historical and current. This chapter therefore aims to describe lantern slide projection as an interactive, ephemeral performance medium, elusive and difficult to categorize, but rich in its creative possibilities.