The evidence in support of there being a genetic component for several disorders related to forensic psychiatry is discussed in the respective chapters. For example, the evidence from twin and adoption studies of the presence of a genetic component in the etiology of psychopathy is given in Chapter 25 (Psychopathy). In this chapter, the focus is on genetic polymorphisms and chromosomal abnormalities rather than on family, twin, and adoption studies. Serious violent offending and antisocial behavior are examples of offending behavior considered in particular here. (Naturally, there is some overlap between these two types of offenses.) The chapter begins, however, with a brief revision of some key terminology in (molecular) genetics.