Attention is a complex neurobehavioral domain that is essential for all higher functions. Large areas of the brain are devoted to attention, reflecting its importance in the entire range of mental operations. Currently, two major distributed neural networks are recognized as mediating complementary aspects of attentional function. One is a diffuse system that distributes attention globally. This attentional system is subserved by a widespread network of thalamic and bihemispheric structures in which the frontal lobes are particularly important. The second network, a focal system that distributes attention to salient aspects of spatial experience, is lateralized to frontal and parietal regions of the right hemisphere. Both attentional networks are comprised of cortical and subcortical gray matter structures, as well as connecting white matter tracts that integrate these regions into functional ensembles. Neurological disorders frequently produce dramatic syndromes reflecting dysfunction of these networks. Among these syndromes are the acute confusional state, which results from disturbance of the diffuse system, and left neglect, which follows disruption of the right hemisphere system. The neuroanatomy of attention is crucial for understanding important neurobehavioral syndromes and their treatment.