The myriad medical breakthroughs predicted to come from the sequencing of the human genome have yet to pour freely. The idea that genes related to common diseases and unique drug responses can be uncovered through careful scrutiny of genetic variation is an inspiring one, but searching for variability remains expensive and time-consuming. A project that would map variants common in most human populations might ease that search. In July 2001, five months after publication of the draft sequence, the National Institutes of Health started planning such a project, now known as the International HapMap Consortium.