Attention research seeks to understand how processing resources are directed to deal effectively with ever-changing internal and external environments. Endogenous attention refers to the ability to voluntarily direct attention based on one’s goals, expectations, or knowledge. Exogenous attention refers to involuntary shifts of attention triggered by salient stimuli in the environment. Both lead to enhanced processing of the information to which attention has been directed. Insight into both the psychological and the neural mechanisms of attention has been greatly advanced in recent years by combining older behavioral approaches with EEG and fMRI that can evaluate brain activity while humans or other animals are engaged in attentional tasks. The widely accepted idea based on these studies of a dedicated attentional system that monitors brain activity and makes decisions about the allocation of neural resources is nonetheless problematic. Many attention researchers recognize this problem and have sought to provide other ways of conceptualizing attention and interpreting the relevant experimental results, but so far without any general agreement among them.