Robert Eustace was the pen name of Eustace Robert Barton (1854–1943), an English doctor and author of mystery and crime fiction with a theme of scientific innovation. He also wrote as Eustace Robert Rawlings. Eustace often collaborated with other writers, producing a number of works with the author L. T. Meade and others. He is credited as co-author with Dorothy L. Sayers of the novel The Documents in the Case, for which he supplied the main plot idea and supporting medical and scientific details.