For centuries, it has been suspected that the vulnerability to psychiatric problems might be heritable. In the 20th century, this was confirmed through twin and family studies, with heritability estimates ranging from ~30-40% for posttraumatic stress disorder and major depression to ~80 for schizophrenia and autism. In the 21st century, genome-wide association studies (GWASs) were introduced, a hypothesis-free design capable of locating DNA associations.<br /><br> AIM: To describe the development of genetic research in psychiatry.<br /><br> METHOD: Overview of selected literature.<br /><br> RESULTS: Increasingly larger GWASs show that the risk for psychiatric disorders is influenced by a combination of environmental factors and the sum of many genetic variants with small effects that combine to explain much variation. A substantial proportion of these genetic effects overlap between psychiatric disorders, but also with positive outcomes, such as IQ and educational attainment.<br /><br> CONCLUSION: We are experiencing a revolution in genetics, in which the sample size, and thus the predictive value of DNA, is growing faster than our understanding of the complexity of the inherited risk for psychiatric problems.<br>.