Tremendous progress in the field of human genetics has made a major impact over the last two decades into our understanding of many Mendelian disorders affecting humans. It is much more difficult to approach the genetics of complex disorders and is particularly challenging in the case of dissecting genetics of the wide range of behavioral variation in the general population. Knowledge of the biology and genetics of Mendelian traits is beginning to inform studies in complex genetics. Furthermore, the convergence of this growing knowledge with increasingly powerful new tools now put complex genetics of behavior within reach. The bottleneck in such studies and the greatest challenge to investigators is the rigorous phenotyping of human research subjects.