This essay provides an overview and reinterpretation of American literary naturalism as practiced by classic naturalists Stephen Crane, Frank Norris, Theodore Dreiser, and Jack London, by later naturalists such as Phillips and Steinbeck, and by those whose contributions to naturalism deserve more recognition, among them women writers and writers of color such as Paul Laurence Dunbar and Ann Petry. The first section defines classic naturalism through four of its key features, each as exemplified by the fiction of one of the major turn-of-the-century naturalists: urban poverty, violence, and parody in Crane; theories of heredity and capitalism in Norris; Social Darwinism and determinism in Dreiser; and racial atavism and primitivism in London. The second section reviews the problems of definition that have formed the critical discourse over naturalism since its inception, including distinguishing naturalism from other literary forms and surveying the late 19th-century controversy over realism and the romance. The third section discusses critical trends in scholarship on naturalism, with particular attention to criticism published from 1980 to the present. To investigate the complex ideological and cultural work of naturalism during its classic phase and into the 20th century, the fourth section theorizes four thematic groupings: space and place, corporeality, mechanisms and technology, and lines and boundaries. When deployed as a series of interpretive lenses, these groupings not only expand the possibilities for reading classic naturalist authors but also provide a means of inclusion for those whose naturalistic writings have been little discussed. Naturalism thus emerges as less as an artifact of literary history to be recovered than as a vital means of interpreting texts across several decades.