INTRODUCTION
This chapter is concerned with people's emotional responses to extradyadic relationships and in particular the hurt that is experienced when they occur. Given the enormous interest in popular culture about such relationships and the potential impact they have on family dynamics, including of course separation and divorce, surprisingly little research has been concerned directly with understanding the patterning and consequences of different forms of extrapartnership involvement. Some related topics have been researched more than others. For example, the incidence of extramarital sex has been examined in a number of studies (Haavio-Mannila & Kontula, 2003; Laumann, Gagnon, Michael, & Michaels, 1994; Treas & Giesen, 2000; Wellings, Fields, Johnson, & Wadsworth, 1994; Wiederman, 1997), as have feelings of jealousy in response to the discovery of a partner's infidelity (e.g., Buss, Larsen, Westen, & Semmelroth, 1992; Buunk & Dijkstra, 2006; Harris, 2003). But there has been limited research explicitly examining the social or psychological impact of extrapartnership involvement, particularly outside clinical settings (Olson, Russell, Higgins-Kessler, & Miller, 2002). Perhaps this is not surprising given the secret as well as sensitive nature of the topic, but as a consequence extensive or detailed information about people's actual experiences of extrapartnership involvement, including the hurt they experience, is not readily available.