In this chapter we have reviewed the diagnosis and management of attention deficit disorder, focusing particularly on the role of stimulant therapy in ADHD. Hisorical review suggests that ADHD has roots that extend back almost a century. The definition of ADHD is based on inclusion and exclusion criteria that are established by history and reflect behavioral concerns. Attention-deficit/hyperactivity disorder is a chronic disorder affecting the child's home, school, and community life. The primary symptoms of the disorder manifest a developmental pattern: activity diminishes while attentional deficits persist. Major sources of concern are the secondary and often more resistant problems of learning difficulties, behavioral problems, lack of peer acceptance, and low self-esteem. An often frustrating and perplexing characteristic of the disorder is its marked variability-over time, across situations, and within the same child and similar situations. Educational management represents an important priority and often forms the cornerstone of all other therapies, nonpharmacologic or pharmacologic. Cognitive-behavioral therapies represent the most widely used alternative to pharmacotherapy. Although the effects of CBT alone are disappointing, recent studies suggest that such therapies may provide a useful adjunct to pharmacotherapy and may be helpful when children are tapered off medication. Psychotherapy, or a combination of psychotherapy and medication (termed multimodality therapy), may also be useful. Pharmacotherapy for ADHD originated almost 60 years ago, and at this time the ameliorative effects of medications in ADHD are well established. The general skepticism of experienced clinicians, coupled with a climate where parents are reluctant to medicare children, serves to limit their use except where indicated. Although the effects of stimulants on attention and activity seem well established, effects on cognition, conduct, and social behavior are more controversial. Within recent years, a great deal has been learned about the pharmacokinetics of stimulants in children with ADHD, providing a rational basis for administration. It is also clear that side effects are minimal, the most serious being the possibility of the emergence of tics. Whereas stimulants are clearly the most effective agents, other agents, including antidepressants, may also be effective. Recent advances may now provide an opportunity to better understand the neural and molecular basis for ADHD. Recent advances in imaging technology, particularly fMRI, offer an opportunity to examine the neural basis of ADHD, and advances in genetics may provide clues to its etiology.