According to this model there are numerous genetic influences on dopaminergic and noradrenergic pathways in the brain. It is also assumed that patterns of activity in these two systems interact, so that activity in each system has some effect on the other. These neural systems in turn are postulated to affect the development and operation of diverse psychological processes, including executive functions, motiva- tional processes related to reward, and potentially other unspecified motivationaV cognitive systems. These processes in turn ultimately explain the symptoms whose ratings lead to a diagnosis of ADHD. Once again we would stress that this diagram is in no way intended to be a complete model of ADHD and its development. The model is incomplete and underspecified in many ways. However, we believe this model gives a different way of thinking about a disorder such as ADHD. In this model the unifying constructs are biological (abnormalities in dopaminergic and pathways) and such abnormalities in neurotransmitter systems may have diverse psychological functions. However, in this view there may not be a unifying psy- chological account for the disorder. This is a slightly disturbing prospect (at least for cognitive psychologists like us) and we have deliberately phrased this alternative in a fairly stark way. In reality, the structure of the psychological mechanisms underlying the development of ADHD may yield a clearer picture if given continued scrutiny