Introductory textbooks on neurogenic communication disorders associated with aphasia and brain injury do not provide full documentation of the pervasive influence of perseveration in the diagnosis and treatment of clients with severe language processing deficits. This special issue of Aphasiology aims to revives the profound interest in verbal perseveration observed in the classical German literature between 1890 and 1931. Various aspects of the phenomenon of perseveration are addressed in this issue. When and under what circumstances do perseverations occur? What are the characteristics of perseverative errors and how do they relate to non-perseverative sound and word errors? The papers share a common goal, namely to understand the origin of the phenomenon `perseveration' in healthy subjects and clients with brain damage and injury. An overarching claim throughout the papers is that perseveration reflects the client's primary language processing deficits.