The majority of research conducted in the field of Attention Deficit/Hyperactivity Disorder (AD/HD) has comprised laboratory-based psychological studies using highly repetitive and boring tasks. Hence, the generalisability of such work is somewhat limited. This book describes, in three sections, a unique research program which successfully sought to achieve ecological validity in research. Specifically, the three sections describe: (i) the historical conceptualisation of AD/HD and the emergence of models of AD/HD; (ii) the development of a unique quantitative research program incorporating studies using a traditional approach through to those conducted in naturalistic settings; and (iii) the initiation of a related grounded theory research approach to bringing about a fuller understanding of the everyday experiences of individuals with AD/HD.