When James (1890) said of attention “everyone knows what it is,” he had in mind a clear, self-evident notion that “implies withdrawal from some things in order to deal effectively with others.” Since then, however, the term attention has been used to mean selection, mental effort, concentration, zind search, and this had led some to claim (Eysenck & Keane, 1990, p. 107) that “there is an obvious danger that a concept that is used to explain everything will turn out to explain nothing.” The danger is a small one, however, and one of the aims of the contributions selected for this special issue of Cognitive Neuropsychology is to show that, far from providing blanket explanations of different phenomena, attention is a phenomenon to be explained. A second aim of the papers is to show that the concept is used as much as a tool for investigation as it is a tool for explanation: To investigate, but not explain, aspects of dyslexia (Whyte) or mental retardation (Merrill & O’DeKirk) and to investigate, but not explain, aspects of frontal lobe function (Foster et al.). The simple fact is that attention is not a unitary function and there are probably as many varieties of attention as there are varieties of memory or learning, neither of which is a unitary function and neither of which is ever said to be in danger of being a useless concept. The third aim of this issue, then, is to present papers dealing with attention as both an explanatory tool and a subject which requires its own explanation. How does attention operate o n objects and their elements (Humphreys & Riddoch, Walsh & Perrett)? Is neglect an attentional deficit (Halligan & Marshall, Humphreys & Riddoch)? And can one tap the activity of brain regions involved in tasks