Introduction to the special section on the concept of disorder.

Despite the absence of a consensual definition of disorder, considerable research and clinical work is based on the categorization and diagnosis of mental disorder. This article introduces a special section of the Journal of Abnormal Psychology that expands the debate between J. C. Wakefield (1999), who has proposed a "harmful dysfunction" analysis of disorder and S. O. Lilienfeld and L. Marino (1995, 1999), who offer an alternative "Roschian" or prototype analysis. This introduction summarizes the main arguments of Wakefield's target article and 8 critiques and discusses the conceptual value of the debate, especially an integration of diverse viewpoints and stimulation to further consideration of this important topic.