The International HapMap Project produced a genome-wide database of human genetic variation for use in genetic association studies of common diseases. The initial output of these studies has been overwhelming, with over 150 risk loci identified in studies of more than 60 common diseases and traits. These associations have suggested previously unsuspected etiologic pathways for common diseases that will be of use in identifying new therapeutic targets and developing targeted interventions based on genetically defined risk. Here we examine the development and application of the HapMap to genome-wide association (GWA) studies; present and future technologies for GWA research; current major efforts in GWA studies; successes and limitations of the GWA approach in identifying polymorphisms related to complex diseases; data release and privacy polices; use of these findings by clinicians, the public, and academic physicians; and sources of ongoing authoritative information on this rapidly evolving field.