Genome-wide association studies (GWAS) uncovered common variants associated with common diseases. As a result of GWAS, more than 300 replicated associations have now been reported for more than 70 common diseases and biological measurements. Although the causal variants still remain unclear in many cases, these genetic association data are now providing a way to understanding the etiology of disease as well as difficult path to better treatment and disease prevention. Because there also exist examples of rare variants influencing common diseases, DNA resequencing of many functionally relevant genes in comparatively large number of individuals will be required to identify causal variants which are not detected by GWAS using common variants as a genetic marker.