In theatre, naturalism is a mode which developed in the late 19th century, influenced by Émile Zola, who wrote the essay Naturalism and the Theatre. A reaction to the contrived, unrealistic narratives which dominated the stage at the time, naturalistic theatre attempted to present a scientific analysis through drama of Man in his natural habitat, responding to the "natural" forces which act upon him. These forces included society, family and heredity.

Naturalism is often confused with realism, in that the naturalist plays pioneered many of the modes of presentation which we now refer to as realist: accuracy of set and costume, faithful reproduction of the speech and manners of ordinary people and, above all, the convention of the fourth wall, placing the audience in the role of outside observers of the characters' drama.

Not all realistic drama is naturalistic, however, as naturalist drama is characterised by preoccupations related to the moral and scientific philosophies of the same name, and is very much rooted in the period of the late 19th and early 20th centuries. The archetypal naturalist play is often identified as Zola's Thérèse Raquin, and other typical examples of the mode would be Ibsen's A Doll's House and Strindberg's Miss Julie. Naturalist drama is also closely associated with André Antoine's Théâtre Libre.