Research studies in psychiatry which take into consideration the gene-environment interaction (GEI) are relatively a new research model. The findings coming from recent studies in the field show that geneenvironment interactions really exist in nature and significantly influence many mental disorders. This article aims to address several problems. First, the authors explain what is meant by gene-environment interaction. Also we discuss why such interactions are so important in psychopathology, and summarize emerging evidence about gene-environment interactions in development of mental disorders. The article focuses on studies of antisocial behavior, because these have been leading the way in investigating environmental as well as genetic influences on psychopathology. The final part of the article envisages future work on gene–environment interplay, arguing that it is an interesting and profitable way forward for psychopathology research.