Posttraumatic stress disorder (PTSD) is common and debilitating. Posttraumatic stress disorder is moderately heritable; however, the role of genetic factors in PTSD etiology has been largely neglected by trauma researchers. The goal of this study is to motivate trauma researchers to reflect on the role genetic variation may play in vulnerability and resilience following trauma exposure. Evidence from family, twin, and molecular genetic studies for genetic influences on PTSD is reviewed. Recommendations for future studies are presented with emphasis on study design and assessment issues particular to the field of trauma and PTSD. Clinical implications of PTSD genetic studies are discussed.