As in all areas of the literature on delusional disorders in their various forms, there is considerable confusion when discussing jealousy and it is not always clear whether authors are describing normal or pathological jealousy or, in the latter case, which associated psychiatric illness they are considering. Jealousy can arise in a variety of contexts but in this chapter we are dealing more or less exclusively with sexual jealousy. Sexual jealousy is virtually a universal human emotion: there have been anthropological descriptions of societies in which sexual partners are exchanged apparently without distress, but this seems to be excessively rare.

Most of us fully understand that jealousy is likely to arise when a rival attempts to attract away an individual's sexual partner. Interestingly, according to Mullen and Martin (1994), men and women tend to react somewhat differently in such a situation. The jealous male is likely to be more concerned about actual loss of the partner, whereas the female is more prone to worry about the effect of infidelity on the quality of the ongoing relationship. Both sexes seem equally prone to experience jealousy, however differently they express it.

There is reasonable consensus that jealousy can occur at three levels of significance.