ADHD is a complex behavioral syndrome with poorly understood causal inputs. The study of cognitive mechanisms has helped shed light on this complexity. Further clarity can emerge from considering temperament and personality as an endophenotype or alternative phenotype for ADHD components. However, the next generation of research has to move beyond merely looking at mechanisms to understand how mechanisms are related to causal factors—specific genes, specific environmental risks, and their interplay. In this lecture Dr. Nigg will highlight key discoveries in the cognitive correlates of ADHD, consider a temperament perspective on vertical integration of biological and cognitive elements in ADHD. New and recent findings will be discussed involving specific genes and specific environments, including toxin exposure and psychosocial stressors, and their interplay in ADHD. These inputs will be related to a multi-component model of ADHD.