emphasizes the emotional nature of close bonds between two people. Bowlby's original theory, which focused on understanding the close, enduring bonds between infants and their caregivers, highlighted two ways in which emotion is implicated in attachment. First, when infants experience emotional distress, they seek proximity to their caregiver. Second, caregivers who are sensitive and responsive are able to help infants regulate their feelings of distress, enabling them to experience an emotional sense of well-being or "felt security" (Sroufe & Waters, 1997). Research on attachment in adult close relationships (e.g., romantic relationships), which are the focus of this chapter, also has highlighted the connection between attachment and emotion (e.g., Kazan & Shaver, 1987;Pietromonaco & Feldman Barrett, 2000). Like children, when adults become distressed in the face of a threat, they may seek out an attachment figure in an attempt to regain an emotional sense of felt security (Simpson & Rholes, 1994).