The vast majority of genome-wide association studies (GWAS) have focused on the main effects of gene variants at specific loci on disease outcomes or traits, although most associations identified so far account for only a small portion of the phenotype variations seen [McCarthy et al., 2008; Hindorff et al., 2009]. To extend these findings GWAS consortia and collaborations have formed in which investigators share data to achieve adequate power to identify genetic loci associated with secondary phenotypes and increase the power to study less common outcomes [Psaty et al., 2009; Manolio et al., 2007]. There have been several single center studies of gene-environment (G*E) interactions in complex disease [Kang et al., 2010; Cornelis et al., 2009] but the development of consortia also offers the opportunity to enhance power to discover and verify G*E interactions. Investigators planning new studies and looking to establish consortia or collaborations can share information on how phenotypes are being measured, what questions are being asked, and how responses will be coded so that similar data can be combined with relative ease. Tools such as the PhenX
