Posttraumatic stress disorder (PTSD) is a relatively common mental health condition that can occur after exposure to a traumatic event. The lifetime prevalence of the disorder in the general population is about 8%, with a 2:1 prevalence of the disorder in women (10%) compared with men (5%; Kessler, Sonnega, Bromet, Hughes, & Nelson, 1995). Although a range of traumatic stressors may cause PTSD, the genesis of most PTSD cases are man-made traumas (Norris, 1992), portending the inherently interpersonal phenomenology and consequences of the disorder. Nonetheless, there have been limited efforts to understand PTSD through an interpersonal lens, despite compelling evidence establishing an association between PTSD and relationship problems. In this chapter, we describe PTSD and its manifestation in adult close relationships, review the empirical literature documenting an association between PTSD and close relationship problems, discuss theoretical constructs and models explaining the association, present various interpersonally oriented PTSD treatment efforts, and consider future directions for research.