Attention-deficit/Hyperactivity Disorder (ADHD) is a neurodevelopmental disorder, characterized by impairing degrees of inattention, disorganization, and/or hyperactivity-impulsivity. Inattention and disorganization involve ones' inadequacy in keeping on task, apparent not listening, and losing materials, at levels that are inconsistent with age or developmental level. Hyperactivity-impulsivity involves overactivity, fidgeting, incapability to stay seated, intruding into activities of others, and incapacity to wait, at levels that are excessive for age or developmental level. ADHD in childhood commonly overlaps with externalizing disorders (e.g. oppositional defiant disorder, conduct disorder). It usually persists into adulthood and leads to social, academic and occupational impairments.