Attention Deficit Hyperactivity Disorder (ADHD) is a neurobehavioral disorder characterized by inattention and hyperactivity-impulsivity that impairs functioning. There are three subtypes - Hyperactive-Impulsive, Inattentive, and Combined - defined by specific symptoms present for at least six months. Possible causes include heredity, pregnancy/birth complications, brain injuries, and environmental toxins. Diagnosis involves onset before age 7, impairment in multiple settings, and ruling out other disorders as the sole cause of symptoms. Parents suspecting ADHD should consult their child's pediatrician and teacher.