In this volume there is a strong emphasis on translational science, with preclinical approaches suggesting new directions for development of new treatments.  Individual chapters describe how neuroimaging, neuroendocrine, genetic and behavioral studies use powerful research tools that are offering a completely new understanding of the factors that increase vulnerability to ADHD.  The clinical impact of co-morbid problems, especially obesity and substance misuse, are highlighted and explain what such problems can tell us about the etiology of ADHD, more generally.  Reviews of the pharmacology of established drug treatments for ADHD justify an exciting novel theory for their therapeutic actions and address questions about the effects of their long-term use.