Attention deficit hyperactivity disorder (ADHD) is a neurodevelopmental disorder that first emerges in childhood, and may continue into adolescence and adulthood. It is characterised by inattention and/or hyperactivity and impulsivity. It was previously known as Attention Deficit Disorder (ADD), but from 2000 the name Attention Deficit Hyperactivity Disorder (ADHD) is now used as it is recognises that there are three main presentations of this disorder. Like all behaviourally defined disorders, the symptoms may change depending on the environment. Unlike many other medical disorders there is no objective way of assessment ADHD (yet), and whilst diagnosis can (and should) include formal objective tests of attention and impulsivity, the core of the assessment is based upon subjective observations of the symptoms below.