This chapter explores both major depressive disorder (MDD) and prolonged grief disorder (PGD) as responses to disasters and terrorist events. MDD should be diagnosed in individuals for whom intense dysphoria and feelings of sadness persist and who experience related depressive symptoms. PGD is more severe and unremitting than normal grief. PGD is associated with considerable functional impairment, physical and mental health morbidity, lost productivity, suicide, and fewer quality adjusted life years. Studies have shown that PGD symptoms form a coherent cluster distinct from bereavement-related depressive and anxiety symptom clusters. Postdisaster prevalence of depression varies considerably across disasters and estimates can be misleading without additional information. Risk and resilience factors can be temporally categorized into three categories: preevent predictors, perievent predictors, and postevent predictors. Grief and depression-focused treatments are rarely implemented systematically in the wake of disasters.