Advances in genetic analysis as well as progress in the Human Genome Sequencing Project have raised the hope to elucidate the molecular basis of mental disorders on the DNA level. In the present review we describe and discuss the basic concepts which are currently applied for the genetic approach in order to find DNA variations associated with a disorder. A prerequisite for such studies is the confirmed evidence for genetic transmission established by family-, twin-, and adoption studies. We describe the study design and discuss the mode of inheritance for complex genetic traits in comparison to monogenic, Mendelian traits. Recombination as a basis for linkage analysis is explained and its implication for classical LOD score analysis in families, as well as for affected sib-pair analysis and for analysis of linkage disequilibrium is discussed. Moreover, we describe types of markers and maps used in these studies. We explain and discuss the association approach in conjunction with the Human Genome Project. Finally, we stress possible implications for diagnosis, prevention and new therapeutic approaches.