This special issue is among the first volumes to examine the topic of early development in children with neurogenetic disorders associated with intellectual disability. It includes discussions of theoretical issues regarding the emergence of behavioural profiles during early development, as well as comprehensive accounts of early development in specific disorders such as Down syndrome, fragile X syndrome, Williams syndrome, and sex chromosome disorders. In addition, several contributions examine the latest clinical applications of this work for diagnosis, treatment, and education. - The comprehensive nature of the reviews of early development in neurogenetic disorders provided by top researchers in the field of developmental disabilities research - Innovation in the application of new approaches to this population, such dynamic systems theory and the developmental trajectory approach to studying these populations place this volume on the cutting edge of theoretical work in this area - This volume also addresses the implications of emerging behavioural phenotypes in neurogenetic disorders from many angles—the biological issues related to diagnosis, psychiatric issues related to comorbid conditions such as autism and autism spectrum disorder, and educational issues related to targeted intervention