Within the last year, genome-wide association (GWA) studies have identified a large number of robust associations between genetic variants and common diseases. Two key premises underlie this burst of discovery. First, the HapMap project has provided a catalogue of human genetic variation. Second, genotyping microarrays can now assess up to 1 million SNPs, allowing hypothesis-free screening of the entire genome. An important next step will be to elucidate the mechanisms behind genotype-phenotype associations. Ultimately, the goal is improved prevention, diagnosis and therapy.