A number of theoretical models of attention-deficit/hyperactivity disorder (ADHD) have emerged in recent years that may be used as systematic guides for clinical research. The cognitive-energetic model (CEM) proposes that the overall efficiency of information processing is determined by the interplay of three levels: computational mechanisms of attention, state factors, and management/executive function (EF). The CEM encompasses both top-down and bottom-up processes and draws attention to the fact that ADHD causes defects at all three levels. These include cognitive mechanisms, such as response output; energetic mechanisms, such as activation and effort; and management/EF deficits. Increasing evidence suggests that inhibition deficits associated with ADHD may, at least in part, be explained in terms of an energetic dysfunction. The activation and effort energetic pools appear most relevant to ADHD, being directly related to response organization; however, further testing of CEM is critically dependent on the development of direct measures of these energetic pools. The CEM is a comprehensive model of ADHD but is not without limitations. In particular, further research is required to define more specifically the relationship between process dysfunction and state dysregulation in ADHD. © 2005 Society of Biological Psychiatry.