Language models are increasingly attracting interest from writers. However, they have limited usefulness for long form creative writing because they lack long-range semantic coherence. We address this limitation by applying language models hierarchically ,in a system we call Dramatron. By building structural context via prompt chaining, Dramatron can generate coherent scripts and screenplays complete with a title, characters, story beats, location descriptions, and dialogue. We illustrate Dramatron’s usefulness as an interactive co-creative system with a user-study of 15 theatre and film industry professionals, who co-wrote theatre scripts and screenplays with Dramatron and engaged in open-ended interviews. We report reflections from our interviewees, and from independent reviewers who watched recent stagings of these works, to illustrate how both Dramatron and hierarchical text generation are useful for human-machine co-creativity. Finally, we discuss the suitability of Dramatron for co-creativity, ethical considerations–including plagiarism and bias–and participation models for the design and deployment of such tools.