This chapter situates Ian McEwan in the history of the novel of ideas, arguing that he reclaims this contested aesthetic space, producing rich and satisfying works. In doing so he pushes the boundaries of literary realism, producing a new kind of hybrid: ideational realism. The essay focuses on four novels – The Child in Time (1987), Enduring Love (1997), Saturday (2005) and Machines Like Me (2019) – a quartet of novels that illustrates the development of ideational realism throughout McEwan’s career. In these novels influential contemporary thinking is pressure-tested in the creative realm: we are invited to question the implications of science as we witness the parameters of the social novel being stretched, adjusted, and re-established. Thus, these novels represent a limited form of experimentalism, in which the significance of scientific ideas is tested, as the social relevance of realist fiction is consolidated.