Recent advances in high-throughput genotyping have made possible genome-wide association studies (GWAS) in which hundreds of thousands of common DNA variants spread across all the chromosomes are examined in a large number of individuals rapidly and for a realistic cost. The GWAS approach has been successfully used to identify common susceptibility variants involved in many non-psychiatric diseases, such as heart disease, diabetes, Crohn's disease, and in normal traits such as height. The typical finding is numerous susceptibility loci, each of which has a small effect size. Genome-wide association studies are similarly providing robust and replicable evidence for genes and, hence, proteins and biological systems/pathways that are involved in the aetiology and pathogenesis of major psychiatric disorders, including schizophrenia, bipolar disorder, attention-deficit hyperactivity disorder, autism and Alzheimer's disease. This article outlines for the busy psychiatrist some of the key messages emerging from this line of research.