Attention-deficit/hyperactivity disorder (ADHD) is a heterogeneous disorder encompassing a wide array of clinical presentations, levels of impairment, etiologies, and neurobiological correlates. Despite this well-known heterogeneity, most research into the pathophysiology of ADHD has relied on comparisons between typically developing youth and those with the disorder (or perhaps further stratifying by DSM-defined ADHD subtypes). Although informative, this approach assumes a level of pathophysiologic homogeneity that belies the large and growing body of literature underscoring diverse neurobiological and neuropsychological profiles subsumed under the umbrella of this complex syndrome. For example, deficits in executive functions are characteristic of ADHD, yet meta-analysis suggests that these deficits are neither necessary nor sufficient to define all cases and that substantial overlaps in levels of executive functioning exist between children with ADHD and their typically developing peers. Likewise, neuroimaging research points to distinct neural circuits underlying different clinical presentations of ADHD, suggesting that, within the diagnosis of ADHD, the neural circuits that are most salient to the disorder can differ from one child to the next. Refining our understanding of ADHD subtypes not only on the basis of symptoms, but also by incorporating neurobiology, physiology, and neurocognitive profiles, could help propel the field toward greater specificity in diagnosis and treatment.