The purpose of this review is to provide an overview of attention as it has been studied in the field of psychology. Broad themes in terms of theory are highlighted, focusing on concepts of attentional resources and attentional effort. In addition, a functional approach to understanding attention is presented, describing attention in terms of the task contexts in which it may operate: selective attention, divided attention, attention switching, and sustained attention. Factors promoting and impairing good task performance in each of these contexts are introduced. Posner's attentional network and Mesulam's attentional matrix are also briefly reviewed in support of the point that attentional functions appear to be distributed throughout the human brain. Topics covered provide a foundation for understanding attention and its role in everyday behavior, as well as a rubric for thinking about and understanding attentional behavior that would be useful in practice.