Convincing demonstrations of association, underscored by the discovery of hundreds of loci for individual traits and disorders such as schizophrenia (SCZ) now come from GWAS of tens or even hundreds of thousands of individuals. We established the PGC-PTSD group in order to accomplish the critical next step in PTSD genetics: to conduct very large GWA studies of PTSD – which only be accomplished by large ‘team science’– combining tens of thousands of samples across cohorts.