This article discusses the text of the work On Simples attributed to Dioscorides. It argues that in fifteen places the transmitted text is faulty, and it proposes emendations. It also studies certain types of insertions made in the text by its most recent editor, Max Wellmann, and concludes that they are unnecessary. Finally, it discusses two points where On Simples sheds light on Dioscorides’ De materia medica.