This essay makes the case for a reconsideration of Theodore Dreiser's An American Tragedy within the history of the modernist novel and its medial legacies by attending to the complex relationship enacted throughout the text between material forms and structures of interiority and identity. Although the mass media and other representational technologies such as cameras and film are notoriously complicit with the deterministic forces propelling An American Tragedy, I show that what counts as the “medial” in the novel appears instead in very different technologies: the stamping apparatus used in the novel's collar factory and the explicit figuring of architectural interiors as technologies of interiority. Both technologies show the process of identification central to the novel's narrative movement to be one of versioning, a media process encoded in the stamping technology and localized in hall ways that behave like characters. The factory tools and architectural spaces populating An American Tragedy, each rendered as a form of mediation, reveal Dreiser's text to hold a more important place in the formal history of the novel and of the novel's relationship to media than it has previously been afforded, especially as that story involves the blurry edges of the modern subject. It is precisely where the novel's naturalist concern with materiality confronts a modernist preoccupation with interiority that An American Tragedy provides a crucial glimpse into the kinds of persons and kinds of mediations developing in the early twentieth-century novel.