Attention deficit/hyperactivity disorder (ADHD) is among the most common neurobehavioral disorders presenting for treatment in children and adolescents. ADHD is often chronic with prominent symptoms and impairment spanning into adulthood. ADHD is often associated with co-occurring disorders including disruptive, mood, anxiety, and substance abuse. 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. Consideration of all aspects of an individual’s life needs 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 ADHD and comorbid problems. Pharmacotherapy including stimulants, noradrenergic agents, alpha agonists, and antidepressants plays a fundamental role in the long-term management of ADHD across the lifespan.