Much of what we thought we knew about genetics needs to be modified in light of recent discoveries. What are the implications of these advances for identifying genes responsible for the high heritability of many behavioral disorders and dimensions in childhood? Although quantitative genetics such as twin studies will continue to yield important findings, nothing will advance the field as much as identifying the specific genes responsible for heritability. Advances in molecular genetics have been driven by technology, especially DNA microarrays the size of a postage stamp that can genotype a million DNA markers simultaneously. The ultimate goal of GWA is to sequence each individual’s entire genome, which has begun to happen.