Attention deficit/hyperactivity disorder (ADHD) is among the most common neurobehavioral disorders requiring treatment in children and adolescents. The disorder is often chronic, with prominent symptoms and impairment spanning into adulthood. It is often associated with co-occurring disorders, including disruptive, mood, anxiety, and substance abuse disorders. The diagnosis of ADHD is clinically established by review of symptoms and impairment. The biological underpinning of the disorder is supported by genetic, neuroimaging, neurochemistry, and neuropsychological data. All aspects of an individual's life need to be considered in the diagnosis and treatment of ADHD. Multimodal treatment includes educational, family, and individual support. Psychotherapy alone and in combination with medication is helpful for treating patients with ADHD and comorbid disorders. Pharmacotherapy, including stimulants, noradrenergic agents, α-agonists, and antidepressants, plays a fundamental role in the long-term management of ADHD.