Purpose of Review: The last decade has generated much interest in the genetics of developmental disorders. This interest, in part, is focused on two issues: the specificity/generality and the type/frequency of the genetic mechanisms involved. Recent findings First, it appears that studies are more fruitful and their results more replicable, broadly speaking, when they conceptualize disorders not holistically, as categorical units, but componentially, through various quantitative processes. Second, there have been several successful investigations of severe impairments in a number of isolated families with higher than typical frequencies of developmental disorders. Yet, it has been difficult to generalize the genetic mechanisms involved in these rare cases to the general population. Summary Current findings suggest the involvement of multiple genetic mechanisms in the manifestations of childhood-onset conditions. It is possible that each 'facet' (or component) of a disorder is controlled by a semi-independent set of genes. Numerous components appear to be deficient in more than one disorder, possibly explaining comorbidity. The genetic foundation of developmental disorders may be formed not by isolated genes, but rather by a combination of genes and the pathways that these genes regulate. These accumulating findings have direct implications for designing both diagnostic and treatment approaches to childhood-onset disorders.