One of the most striking developments in the framework of biological psychiatry, is the use of human as well as animal genetics’ methodology in psychiatrie research. After reviewing some basic concepts in human genetic research, we shall present the current status of our knowledge on the genetic’ determinants of the major psychoses, i.e., the affective psychoses and schizophrenia. The importance of genetic research into psychiatry can also be underscored from a biometric point of view in showing its contribution to the clarification of problem of nosology in attempting to subclassify abnormal behavior on a more etiological ba