Family and twin studies have revealed that genetic factors play a major role in psychiatric disorders, however, attempts to find susceptibility genes for these complex disorders have been largely unsuccessful. Therefore, new research strategies are required to tackle the complex interactions of genes, developmental, and environmental events. Here, we will address a behavioural domain concept that focuses on the genetics of behavioural domains relevant to both animal behaviour and across human psychiatric disorders. We believe that interspecies trait genetics rather than complex syndrome genetics will optimize genotype-phenotype relationships for psychiatric disorders and facilitate the identification of biological substrates underlying these disorders.