This article describes the current clinical view of attention-deficit/hyperactivity disorder (ADHD) and suggests a model of prefrontal lobe executive functions that explains better than current theories the cognitive and behavioral deficits associated with ADHD. The model shows how behavioral inhibition is related to and necessary for the proficient performance of four executive functions that subserve self-regulation: nonverbal working memory; the internalization of speech; the self-regulation of affect, motivation, and arousal; and reconstitution. These functions permit the construction, execution, and control of behavior by internally represented information, which removes behavior from control by the immediate context and brings it under the control of time. ADHD disrupts this process and returns control of behavior to the temporal now. A blindness to past, future, and time more generally, as well as an inability to direct behavior toward the future and to sustain it are among many of the deficits predicted by this model for persons with ADHD.